Set a large pot of salted water to boil and preheat oven to 375° F.
Add the lasagna noodles to the boiling water and cook for 12–14 minutes, or according to package instructions, stirring occasionally. Remove the noodles from the water. Run under cool water to stop cooking, and drain.
While the noodles are cooking, saute the diced onions on low heat with a little cooking oil and a pinch of salt in a large sauté pan until tender—approximately 10 minutes.
Transfer about one-third of the cooked onions to a sauce pan. Add the diced tomatoes and bring to a simmer, then reduce to low. Season with approximately 1 teaspoon Italian seasoning, the fennel seed, and add salt and pepper to taste. Stir in vinegar and keep warm.
Meanwhile, add the garlic and spinach to the onions remaining in the sauté pan and cook over medium heat until the spinach has wilted. Transfer the mixture to a strainer and gently press out any excess moisture. Return the spinach to the sauce pan.
Add the shredded chicken, ricotta, and mozzarella to the spinach and stir to blend. Season with the remaining Italian seasoning, salt and pepper to taste. Allow the mixture to cool slightly, then stir in the beaten egg and combine well.
Lightly grease a large lasagna baking pan then spoon a small amount of the tomato mixture on the bottom of the pan.
Spread 1/4–1/3 cup of the chicken-spinach-ricotta mixture in a thin layer over each lasagna noodle, then carefully roll them up. Line up the lasagna rolls in the baking pan seam-side down. Pour the remaining tomato mixture on top. Distribute the Parmesan cheese evenly over the top, then place the pan in the oven and bake for 25–30 minutes, or until completely heated through. Serve hot. Makes approximately 6 two-roll servings.