Heat the olive oil over medium-heat in a medium sauce pan, add in the diced onions and saute until the onions are translucent. Stir in the crushed tomatoes, minced garlic, dried basil, dried oregano, and dried parsley. Cover with a lid and allow the sauce to simmer for at least 20 minutes over low-to-medium heat.
While the tomato sauce is simmering, prepare your lasagna noodles according on the directions on the back of the package. Once they are done, drain the water and allow the noodles to cool to touch. Preheat oven to 375 degrees.
Prepare your filling by mixing together the spinach, ricotta cheese, 1 and ½ cups mozzarella cheese, parmesan cheese, and egg. Set aside.
Once the noodles have cooled to touch, lay the noodles down on parchment or wax paper on a smooth surface. See photos below.
Spread ¼ cup of the cheese filling evenly along length of the noodles. Roll the noodles to the opposite end. Pour 1 cup of tomato sauce into the bottom of a 9 x 13 baking dish. Place the lasagna roll-ups into the baking dish, add remaining tomato sauce on top of each roll-up. Place the remaining 1 cup of mozzarella cheese on top. Bake for 25 minutes, or until cooked through.