Combine beans, salsa, cumin and chilli powder in large pan. Cook over medium-high heat for about ten minutes, mashing beans slightly with back of wooden spoon. Stir occasionally, adding a little water if mixture looks too dry.
Spoon bean mixture into tortillas. Top with cheese. Fold each tortilla into an envelope shape, ensuring both ends are tucked in. Eat warm or wrap in cling film to take for lunch.