Grease the insert of the slow cooker with cooking spray. Set aside.
Heat up the olive oil in a large skillet set over medium-high heat. Add the onions and cook for 3 minutes, stirring frequently.
Stir in the garlic and cook for 30 seconds, or until fragrant.
Add in the ground beef and continue to cook until no longer pink.
Stir in the tomato sauce.
Add the water, and season with thyme, rosemary, Italian seasoning, salt, and pepper.
Cook for 2 more minutes and remove from heat.
Layer a quarter (¼) of the meat sauce on the bottom of the slow cooker insert.
Top with 3 lasagna noodles, breaking them up so they fit.
In a small bowl combine the ricotta and feta cheese; stir until incorporated.
Spread ⅓ of the ricotta on top of the noodles; sprinkle with ¼ cup parmesan and ½ cup mozzarella cheese.
Repeat the entire process with 2 more layers, finishing with the beef-tomato sauce layer on top, and reserve ½ cup shredded mozzarella cheese for later.
Cook on LOW for 4 hours, or until noodles are tender.
Remove lid and sprinkle the remaining shredded mozzarella cheese on top; cover and continue to cook for 4 more minutes, or until the cheese is melted.
Turn off heat, remove lid, and let stand about 10 to 15 minutes.
Cut and serve.