Heat oil in a large pot over medium-high heat. Add the chopped onions and green peppers and sauté for about 3 minutes until softened. Stir in the garlic and cook for another 30 seconds until fragrant. Transfer the mixture to a 6-quart slow cooker.
In the same pot, cook the ground beef and sausage until fully browned, breaking it up as it cooks. Drain most of the fat, leaving about 2 tablespoons in the pot for added flavor. Transfer the meat to the slow cooker with the with the sautéed aromatics.
Stir in the tomatoes, tomato sauce. green chillies, beef bouillon, and all the seasonings: chili powder, Worcestershire sauce, cumin, paprika, cocoa powder, onion powder, garlic powder, salt, sugar, and black pepper. Cover and cook on low for 6 to 8 hours or high for 2 to 3 hours.
Once the chili is tender and flavourful, stir in the kidney and black beans. Let them warm through for 2 to 3 minutes. Ladle into bowls and serve hot with toppings like sour cream, shredded cheese, cornbread, or tortilla chips.
Notes
Chili can be made 2 days ahead. After cooking, allow to cool completely, cover and refrigerate. On the day of cooking, take out of the refrigerator at least an hour before heating.