Brown the ground beef or turkey in a skillet over medium heat; drain excess fat.
Transfer the meat to the crockpot.
Add chopped onion and minced garlic to the crockpot.
Pour in the diced tomatoes and tomato paste; stir well.
Add the drained beans to the mixture.
Sprinkle in chili powder, cumin, salt, and pepper; mix thoroughly.
Cover and cook on low for 6-8 hours or high for 3-4 hours.
Stir occasionally, if possible, to blend flavors.
Taste and adjust seasoning as needed before serving.
Serve hot, garnished with your choice of toppings like sour cream or cheese.