Mince the onion. Heat olive oil in a medium deep pot over medium low heat. Add the onion and cook until lightly browned, about 5 minutes.
While the onion is browning, roughly chop the baby spinach and cilantro. Add the spinach into the pot and cook just until it wilts.
Add all three cans of beans, the salsa, vegetable broth, cilantro, salt, and diced green chiles (if using) into the pot. Turn the heat up to high and bring to a boil. Cover, and lower the heat to medium high. Allow the chili to cook until thickened into a soup, around 20 minutes.
Right before the chili is done cooking, dice the avocado and add it into the pot.
Transfer the chili into bowls and serve with your favorite toppers.