Jamie Oliver's Diner, 23a Shaftesbury Avenue, London

Avocado fries? Oh, here we go, more Jamie Oliver "reinventing things" (shudder). My last JO experience was at Union Jacks, his pizza venture where the reinvention included such aberrations as Stilton and pork-crackling "flatbread". I was not, it's fair to say, impressed and gave it one of my lowest-ever scores.

So it is with mixed feelings that I approach the Diner, a two-year pop-up in London's West End. Jamie Oliver jumping on two bandwagons at once (ouch!) – that of the pop-up and of the haute burger/hot-dog movement – could be simultaneously bad news for my dining pleasure and good news for my critical eye.

The site is at the unlovely meeting of Shaftesbury Avenue and Piccadilly Circus, and was once a thing called Adam's Rib. It is perfect for the tourists who mill about this area looking for "the London scene", blissfully unaware that it's happening mere steps from them, on Soho's back streets (Pitt Cue Co, Polpo), and a few Tube stops away in Shoreditch and Dalston (Clove Club, Rita's).

At street level, a take-out stand – the Dog House – has the raw wood and galvanised steel that will be familiar to fans of, er, lots of other places that do similar food. The idea of getting a decent "dog" while on the hoof in Theatreland is cute, though.

A greeter at the next doorway points you to the greeter at the top of the stairs (how's his job satisfaction, I wonder?). This one asks whether we have a reservation. Oh, do you take them, I ask. No, she replies, but you might be someone special. Not quite sure how to take that… From then on, the staff couldn't be lovelier. Our waiters are effusive and borderline cheeky (they've drunk the Oliver KoolAid) but it's thanks to Francesco that I try those avocado fries.

In honesty, I order them from the rough-printed, diner-by-numbers menu expecting a fatty, flavourless heap of clag. Of the sides on offer (all at £4), they are the most bonkers; shoestring fries and 10-veg rainbow 'slaw the most expected. Hungry as horses, we order chicken in a basket with fries and 'slaw (a pricy £15) and a beef burger with extra Gruyère and sticky balsamic onions (£10 plus £1.50 per extra topping) and some "diner baked beans".

While we wait (and wait – it's day one of proper service), we look around. The diner theme has been visually punned with dinosaurs (geddit?!) everywhere we look – in artwork, statues, even a tapestry. Plus the ubiquitous metal trays and (artistically) sloppy paint job. Cloudy lemonades and a floor-to-ceiling window view of the passing hordes keep us occupied; plus the fascination of who's coming in. It's tourists, yes, for the JO name, but also a few office workers in pairs and solo, for a lunchtime blowout.

And blowout it turns out to be. The chicken is huge, a wire basket with a towering tangle of fries, with almost a whole chicken's worth of tender breast meat, coated in a salty, paprika-y seasoning. It is – sorry Colonel – finger-licking good. And if the fries are a tad soft from their blanket of chook, they still do the job.

Mr M's burger is in a glazed bun, speared with a large green pickle. Nice. The meat is as regulation these days, cooked through. Beans are a medley of chick, kidney and borlotti with a breadcrumb topping. Decent.

Those avocado fries? Wedges, coated in a densely seasoned polenta crumb and very lightly fried, are clever and moreish. Somebody in the kitchen (I can't see whether noted head chef Arthur Potts Dawson is in) cares enough to treat the avo gently.

Before we've put down our forks, a manager comes over to offer us a discount as we had to wait for so long. He's not Jamie Oliver, but near as dammit – cheery, in trucker cap and checked shirt with a bit of stubble. Nothing here is original, from the dishes to the styling, although the prices are several notches above nearby dude-food joints.

This is no indie vibe (I don't believe for even a second that it's a pop-up as much as market research for a new chain). But it's better than so many tourist traps it rubs shoulders with, even if it was probably invented by a box-ticking committee.

7/10

Jamie Oliver's Diner, 23a Shaftesbury Avenue, London, W1. Tel: 020 3697 4117. £50 for two, including soft drinks

Three more tourist favourites

Casa Don Carlos

Always heaving, but feeling like the real deal – this great tapas place in the heart of the Lanes is a friendly spot.

5 Union Street, Brighton, tel: 01273 327 177

Deeson's

Excellent food right next to the cathedral; with its imaginative cooking, it delivers every time.

25-27 Sun Street, Canterbury, deesonsrestaurant.co.uk

Bettys

A 1920s teashop fantasy; highly priced but its standards – not least its classic Anglo-Swiss dishes – are impressive.

6-8 St Helen’s Square, York, bettys.co.uk