Cook lasagna noodles as per package instructions in a large pot of salted water. Then drain and lay flat on a baking sheet. Cover with a towel to prevent from drying out and set aside.
Preheat large skillet on medium-high heat and add ground beef. Cook for 10 minutes, constantly breaking into small pieces and stirring, and draining fat at the end. Add marinara sauce, bring to a boil, cover and simmer for 15 minutes.
In a large bowl, add cottage cheese, egg and Italian seasoning. Stir to combine and set aside.
Preheat oven to 375 degrees. Spray large 9×13 baking dish with cooking spray and spread a bit of meat sauce to cover the bottom. Layer 4 noodles lengthwise overlapping a bit. Then spread 1/3 of the meat sauce, 1/2 of the cottage cheese mixture, half of spinach and 1 cup of Mozzarella cheese. Repeat this layer one more time.
Finish with remaining 4 noodles, 1/3 of meat sauce and 2 cups of cheese. Spray aluminum foil or silicone lid with cooking spray to prevent cheese from sticking to it. Bake covered for 25 minutes, then uncover and bake for 20 more minutes.
Remove lasagna from the oven and let stand for 20 minutes while covered. Then using a sharp knife cut into 9 slices and serve using a flat sturdy spatula.
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Notes
Store: Refrigerate leftovers in an airtight container for up to 5 days.
Freeze: Freeze individual slices in a container for up to 3 months. You can also freeze unbaked assembled lasagna!Assemble, tightly wrap with plastic, then few layers of foil, and freeze for up to 3 months. Thaw in the fridge overnight and bake as per instructions adding 10 minutes.