Dice your onion into whatever size you like. This will be a slow cooker meal, so they will be tender regardless.
Place lentils in slow cooker, followed by broth (or water and boullion), onion, and top with chorizo sausage.
Cook in slow cooker on low for 6-8 hours. Alternately, if you are using frozen sausage, place in instant pot and cook on manual for 30 minutes, letting it depressurize manually.
Serve with rice and enjoy!