In a large pot, combine beans, onions, 1 teaspoon garlic and 5 cups water and cook over medium heat for 20 minutes.
Meanwhile, in a separate large pot, warm the olive oil over moderate heat. Add the onions, peppers and remaining 1 tablespoon garlic and cook for 2 minutes.
Add in the tomato sauce, ½ cup water, and chili, cumin, oregano, and cayenne.
Once beans are cooked, drain and discard the bean broth. Place beans in the pot with the veggies and cook on medium heat, covered, for 25 minutes. Season with salt and pepper. Garnish with avocado cubes and serve.