Lightly coat the inside of the crock pot with cooking spray.
Spread 1 cup tomato sauce on the bottom of the pot.
Arrange a layer of the no-boil lasagna noodles over the sauce. Set aside.
In a large mixing bowl, combine ricotta cheese, feta cheese, salt, pepper, chopped garlic, oregano, parsley and eggs; mix until thoroughly combined.
Add spinach and mix until well incorporated.
Spread 1/3 of the ricotta mixture over the pasta.
Sprinkle a layer of mozzarella and 1/3 of the parmesan cheese over the ricotta mixture.
Top with a cup of tomato sauce.
Repeat these layers until all the ingredients have been used up .
Top the lasagna with a layer of lasagna noodles covered with tomato sauce and sprinkled with mozzarella and parmesan cheese.
Cover and cook on HIGH for 3-1/2 to 4 hours.
Turn off the crock pot and let stand 45 minutes, or until all the liquid is absorbed.
Cut and serve.