To make salsa:
Fry the chopped onion and garlic until soft. Add the cumin and tomatoes and cook until broken down and cooked, but not until too dry that it burns. Puree the salsa using an immersion blender. Set salsa aside until later.

To make chicken:
Lay out chicken legs in a single layer in a big frying pan. Cook chicken with about 1cm deep layer of water. Cover the frying pan with a lid. Also, every few minutes stir the legs so that the legs on the outside get towards the heat in the middle. Add tiny bits of water as necessary to keep the pan from going dry until 85% cooked. (Should be firm, i.e. almost all white when poked with knife.)
Then, now that the water has cooked away, add a little oil to fry the chicken for a minute or two.

Add the salsa to the chicken until the whole combination thickens, a few minutes max. Check chicken is done. Serve.