Transfer onion mixture to a large slow cooker. In same skillet over medium heat, break up beef; season with salt and black pepper. Cook, undisturbed, until mostly browned, about 5 minutes.
Throw Everything In: Put all the ingredients in the slow cooker. How Long to Cook Lentil Soup in Slow Cooker: Cook on high for 4 hours or low for 8 hours. Final Touches: Shred the chicken with 2 forks ...