Step 1

For the sauce: In a large saucepan, heat the oil. Add the onions and cook until softened, about 3-5 minutes. Add the garlic and cook 1 minute. Add the tomatoes with juices, basil, oregano, thyme, salt, and pepper. Simmer covered for 20 minutes or until tomatoes break down and sauce starts to thicken, stirring occasionally.

Step 2

Remove from the heat. Very carefully add the sauce to a blender. Blend until smooth. Caution - hot mixtures tend to expand more when blended, so you may need to blend the sauce in two batches so it doesn't splash everywhere.

Step 3

Preheat oven to 375F. Have a 13x9 pan ready.

Step 4

Bring a large pot of water to a boil. Cook the lasagna noodles for 10 minutes. Drain and let cool.

Step 5

In a large deep skillet, heat the olive oil. Add the onion, carrots, and mushrooms and cook until softened, 3-5 minutes. Add the garlic and cook 1 minute. Stir in the ricotta, spinach, and salt until smooth. Cook another 5 minutes or until heated through.

Step 6

Spread a few spoonfuls of sauce in the bottom of the 13x9 pan. Add 3 noodles flat on top, making 3 rows. Add 9 mozzarella half slices on top. Spoon half of the ricotta filling on top then cover with 1/3 of the remaining sauce. Sprinkle 2 tablespoons Parmesan cheese on top. Top with another 3 noodles.

Step 7

Repeat with another 9 half cheese slices, the rest of the ricotta filling, another 1/3 of the remaining sauce, and 2 tablespoons Parmesan cheese. Finish with the remaining 3 noodles, the rest of the sauce, the remaining 2 tablespoons Parmesan cheese, and remaining 10 half cheese slices.

Step 8

Cover with foil and bake for 30 minutes. Remove the foil and bake uncovered for another 15 minutes or until the cheese is melted on top and the lasagna is hot. Cool for 10 minutes then serve immediately.