Spread a thin layer of marinara sauce (about 1 cup) on the bottom of the crock pot.
Add half of the browned ground beef, spreading it evenly.
Place a layer of uncooked ziti pasta over the meat.
Drop spoonfuls of the ricotta mixture over the pasta, spreading slightly.
Sprinkle mozzarella cheese on top.
Repeat the layers two more times, ending with a generous layer of marinara sauce, mozzarella cheese, and Parmesan.