Use a 6-quart slow cooker. Heat a large skillet on the stovetop and brown the ground turkey over medium heat, stirring to break up any clumps. Discard any accumulated fat.

Pour the jar of pasta sauce into the skillet (save the jar!). Ladle a scoop of this meat sauce into the slow cooker insert. Add a layer of lasagna noodles. You may need to break them to get a good fit. Smear some ricotta onto the noodles and add a handful of the shredded cheese. Repeat the layers until you run out of ingredients.

Put the hot water into the pasta sauce jar, seal it, and shake. Pour the liquid evenly over the top of the lasagna. Cover and cook on low for 6-7 hours or until the noodles are bite-tender, the cheese has fully melted, and the top has begun to brown and pull away from the sides. Uncover and let it sit in the cooling cooker for 15 minutes before serving.