Combine everything in the slow cooker. Add all ingredients to the slow cooker onion, garlic, bell pepper, vegetable broth, fire-roasted tomatoes, both cans of drained beans, dried lentils, tomato paste, and all spices. Give everything a thorough stir to distribute the spices evenly through the liquid.
Cook. Place the lid on the slow cooker. Cook on low for 8 hours or high for 4 hours until the lentils are completely tender and the chili has thickened to your liking.
Taste and adjust. Once fully cooked, taste the chili and season with salt and pepper as needed. Remember that the sodium in your broth, beans, and tomatoes all affect the final salt level always taste before adding anything.
Serve hot. Ladle into deep bowls and add whatever toppings you like. The chili is ready to eat immediately and tastes even better the next day.