Plugin your slow cooker and let it heat up for 5 minutes. While you're waiting, dice the onion.
Add the 2 tbsp olive oil to the slow cooker.
Add the onions and cover the slow cooker. Let the onions simmer and mingle with the olive oil for at least 10 minutes. If you can do this for an hour, that's even better!
Add the bell peppers and garlic to the slow cooker.
Then add the black beans, pinto beans, and chili beans. (If using dried pinto beans and black beans, add the vegetable broth. Also, add the vegetable broth if you prefer a chili with more liquid. If using canned beans, the moisture from the can and tomatoes is enough and you don't need the vegetable broth!)
Add the 2 tbsp of chili powder, 1 tbsp cumin, and 1 tbsp garlic salt.
Cook on low for 6 hours on low (especially if you're using dried beans) and enjoy!
Add toppings of your choice and season with salt and pepper as necessary.