In a skillet over medium heat, brown the ground beef or turkey until fully cooked. Drain any excess fat and transfer to the slow cooker.
Add the diced onion, garlic, bell pepper, kidney beans, black beans, diced tomatoes, tomato sauce, corn, chili powder, cumin, paprika, salt, and pepper to the slow cooker. Stir until well combined.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the vegetables are tender and the flavors meld together.
Before serving, taste and adjust seasoning if necessary.
Serve hot, topped with shredded cheddar cheese, a dollop of sour cream, and chopped green onions.