Start by heating a tablespoon of olive oil in a large skillet over medium-high heat. Once hot, add the ground beef, diced onion, and minced garlic. Cook for about 5-7 minutes, stirring frequently, until the beef is browned and the onions are softened.

Transfer the beef mixture from the skillet to your slow cooker. Add in the canned diced tomatoes, drained kidney or black beans, and chopped bell peppers. Sprinkle in the chili powder, cumin, salt, and pepper, then stir everything well.

Cover the slow cooker with its lid and set it to cook on low for 6-8 hours or on high for 3-4 hours.

Once the cooking time is up, give your chili a good stir. Taste and adjust seasonings as needed. Garnish with shredded cheese, a dollop of sour cream, or fresh herbs for added flavor.