Start by bringing a large pot of salted water to a rolling boil. Carefully add the lasagna sheets and cook them according to the package instructions until al dente, about 8-10 minutes. Drain and lay flat to prevent sticking.

In a mixing bowl, marinate the chicken tenders with olive oil, salt, pepper, and Italian seasoning. Heat a skillet over medium-high heat and cook the seasoned chicken for about 4-6 minutes per side until golden brown and cooked through. Chop into bite-sized pieces.

In the same skillet, melt butter over medium heat and sauté onion and garlic until fragrant, about 2-3 minutes. Add flour and stir, then gradually whisk in milk and cream. Allow to thicken for about 5 minutes. Stir in spinach and Parmesan.

Preheat oven to 375°F (190°C). Lightly grease a baking dish. Layer Alfredo sauce, lasagna sheets, chicken, and mozzarella. Repeat layers, finishing with sauce and mozzarella on top.

Cover with foil and bake for 40 minutes. Remove foil and broil for 2-3 minutes until cheese is bubbly and golden. Let rest for 15 minutes before slicing.