Easy Sheet Pan Lasagna

1. Preheat the oven to 425 degrees F. Oil 12 x 17-inch baking sheet with olive oil. 2. Heat a medium skillet over medium heat. Add 1 tbs. oil along with the garlic and pepper flakes. Cook 1 minute. Add the spinach and the salt and cook. Remove spinach to a strainer and press firmly to remove any excess liquid. Add spinach to medium bowl, Add ricotta cheese, stir to combine. Set aside. 3. Add the remaining 2 tbs. of oil to skillet with the sausage and cook, until the sausage is beginning to brown about 3mins. Break apart the sausage into bite sized pieces. Add the onion to the pan and cook until the onion has softened. Remove from heat. 4. Bring large pot of water to a boil. Season with salt. Cook pasta for 4 minutes stirring often. Drain well, reserving 1/2 cup of pasta water. 5. Add the sausage, onion and marinara to a large bowl and mix well. Add the pasta water, pasta, 1 cup mozzarella cheese and 1/2 cup parmesan cheese to the same pan and stir to combine. 6. Spread mixture on baking sheet. Dollop with the ricotta-spinach mixture, and sprinkle with remaining 1 1/2 cups mozzarella and 1 cup parmesan cheeses. Bake 30 minutes. Remove from the oven and let rest for 5mins before serving.