In a large skillet over medium-high heat, brown the ground protein until fully cooked through; drain any excess fat.
Transfer the cooked meat into a 6-quart or larger slow cooker.
Add the rinsed lentils, black beans, kidney beans, crushed tomatoes, onion, bell pepper, and broth to the slow cooker.
Stir in the chili powder, cumin, smoked paprika, garlic powder, onion powder, salt, and black pepper until well combined.
Cover and cook on the Low setting for 7 to 8 hours, or on the High setting for 3 to 4 hours, until the lentils are tender and have absorbed most of the liquid.
Taste and adjust salt or pepper seasoning as needed before serving.