Based in Brixton market is the popular Honest Burger chain. It is a small restaurant so you will no doubt have to queue, however they have a great system where they log your name on their iPads and then text you when you table is ready. They always give you an estimated time that the table will be ready so this gives you more time to wander around Brixton Village/Market Row.
Simple but effective menu: plain burgers, cheese and bacon, chicken, vegetarian and special burgers the restaurant changes every now and again. All burgers served in a glazed bun with fries. Decent burger but I actually prefer Bryon and Meat Mission (see separate reviews). All between £8-12.