In a skillet over medium heat, brown the ground beef or turkey until fully cooked. Drain excess fat and add the cooked meat to the slow cooker.
Add the diced onion and minced garlic to the slow cooker, mixing them with the meat.
Stir in the black beans, kidney beans, corn, diced tomatoes (with juice), diced green chilies, and broth.
Sprinkle in the taco seasoning, chili powder, cumin, salt, and pepper. Mix everything thoroughly until well combined.
Cover the slow cooker and set it to low heat, cooking for 6 hours. If you're short on time, you can set it to high heat for 3 hours instead.
Before serving, taste and adjust seasonings if needed.
Serve hot and allow diners to add their favorite toppings like cheese, sour cream, avocado, and cilantro.