I also do a really good lasagna in my crockpot and it makes a LOT!!
Cook your burger/tomato sauce, onions, etc in a skillet adding extra sauce or broth to thin it.
Begin by layering some sauce on the bottom, add uncooked noodles to the bottom, then a layer of sauce, ricotta and other cheese, then repeat until the sauce is used up or the noodles are gone or the pot is full. Use all the sauce because the uncooked noodles will absorb most of the liquid. Cover and cook on high for 4-5 hrs or on low for 8 hrs.