Cook the lasagna noodles according to package directions and drain.
In a skillet or pot, cook onion in olive oil over medium heat until soft, about 5 minutes. Add sliced mushrooms and garlic, continue cooking until mushrooms are done, about 5 more minutes.
Add diced tomatoes, spaghetti sauce, oregano and pepper to taste to the mushroom and onion mixture. Simmer for 5 more minutes and then remove from heat.
In a large bowl, combine egg, cottage cheese, parmesan cheese, feta cheese and spinach.
Spoon a little of the sauce in a 9x13 glass baking dish the layer in this order:
3 lasagna noodles.
1/2 of the cottage cheese mixture.
1/3 of the sauce.
3 lasagna noodles.
1/2 of the cottage cheese mixture.
1/3 of the sauce.
3 lasagna noodles.
1/3 of the sauce.
Mozzarella cheese.
Cover with foil and bake at 350 degrees for 40 minutes, uncover and continue cooking for 20 more minutes until cheese is light brown and bubbly.