Dice the onion and mince the garlic. Add the onion and garlic to the slow cooker along with all the other ingredients and stir to combine.
Place a lid on the slow cooker and cook on high for four hours (or low for 8 hours). After cooking, the lentils should be tender. Taste the chili and add salt to taste, if needed (this will depend on the salt content of your broth).
*I like to use coconut oil because it has a similar mouth feel to animal fat, but it does give a slight coconut aroma to the chili. Feel free to use your favorite oil or fat in its place.