Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 5 minutes.

Add minced garlic and bell peppers; cook for another 3-5 minutes, until slightly tender.

Add ground beef to the skillet and cook, breaking it up with a spoon, until browned. Drain off any excess grease.

Transfer the beef and vegetable mixture to your slow cooker.

Add crushed tomatoes, tomato sauce, kidney beans, pinto beans, black beans, green chilies, chili powder, cumin, oregano, garlic powder, cayenne pepper, salt, and pepper to the slow cooker.

Stir to combine. Cover and cook on low for 6-8 hours, or on high for 3-4 hours, or until heated through and flavors have melded.

Serve hot, with your favorite toppings such as shredded cheese, sour cream, chopped onions, and avocado.