A couple of central line stops further than I normally go, The Gallery Cafe's both not that far from The City and perfectly located for visiting along with the V&A Museum of Childhood (which is free and highly recommended).
I've been a couple of times in the past year - food, price, waiting time and service all reasonable.
As the name suggests the food and set up is cafe style. Everything's vegetarian and mostly vegan. They've a mixture of communal and individual tables, with a small outside space. On our most recent visit we had a couple of vegan pizzas, which including drinks came to about £20:
Liberal serving of Cheezley and sensible amount of toppings. Fresh dough and crispy base - not stunning but above average.
I'll both return and happily recommend it - whether you're in the area already or fancy a change from the usual Z1 dross.
1 hour ago