Heat oil in a large frying pan on medium high heat. Gently fry onion and garlic for 5 minutes, or until soft and translucent. Stir in chilli powder and cumin, and cook 1 minute. Stir in tomatoes, kidney beans and salt. Bring to the boil, then reduce heat and simmer for 20 minutes.
Stir in spinach and cook 5 minutes more.
Warm tortillas according to packet instructions. Spoon 1/4 of the bean mixture into the middle of each tortilla, fold in one end and wrap. To serve, garnish with avocado, sour cream and salsa.