Place the onions, carrots, mushrooms, garlic, beans, San Marzano tomatoes, water, chili powder, cumin, Adobo Chiles and salt in a crock pot. Stir and cover. Heat on low for 6 hours or high for 4 hours.
When the bean mixture is done, assemble the tacos. Lay out two corn tortillas. Layer the bean mixture, California walnuts, chopped cabbage and carrots, juice of half a lime, and a slice of avocado on top of the tortilla. Enjoy!