Tomato, spinach and bean burrito

2 tablespoons olive oil
1 cup diced onion
3 cloves garlic, minced
2 tablespoons chili powder, or to taste
1 teaspoon ground cumin
1/4 cup water
4 cups chopped fresh tomatoes
1 (15 ounce) can kidney beans, drained and rinsed
salt to taste
1 (10 ounce) package frozen chopped spinach, thawed and drained
4 (10 inch) flour tortillas
1 ripe avocado, sliced
4 tablespoons sour cream
4 tablespoons salsa

Heat oil in a large skillet on medium-high heat. 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.