Saute onion and garlic for 5 minutes. Stir in chili powder and cumin, and cook 1 minute. Stir in water, tomato, kidney beans and salt. Bring to a boil, then reduce heat and simmer for 20 minutes.
Stir in spinach and cook 5 minutes more. Spoon 1/4 of the bean mixture into the middle of a warm tortilla. Wrap and garnish with avocado, sour cream and salsa.