About a hundred good restaurants in Brixton these days. If you can get down early, just go into the market and take your pick.
Or you could go Portuguese on Stockwell Rd. Cantinho De Porto gets a good forum vote.
Nandos, Wahaca and Brindisa from a chain perspective.
Asmara Eritrean is a favourite of mine, on coldharbour lane. Cocktails and tapas next door at 384, but that needs booking probably.