Preheat oven to 350 degrees Fahrenheit. Bring a large pot of salted water to a boil and cook lasagna noodles until al dente. Drain.

To make the spinach, heat oil in a large skillet over medium heat. Add onion and garlic and season with salt, pepper, and red pepper flakes. Cook until onions are soft, about five minutes. Add spinach and cook until wilted. Remove from heat and set aside.

Mix ricotta cheese, eggs, and Parmesan in a large bowl. Season with salt and pepper.

Spread ricotta mixture onto one side of each lasagna noodle. Top with marinara sauce and cooked spinach, then sprinkle with mozzarella cheese and roll up tightly.

Spoon a layer of marinara sauce over the bottom of a large, deep baking dish. Add lasagna roll-ups and spoon more sauce over each roll-up. Sprinkle more mozzarella over the top. Cook until bubbly and melted, about 20 minutes.

Garnish with parsley before serving.