Preheat the oven to 375 degrees F (190 degrees C). Grease a 9x13-inch casserole dish with nonstick spray.
Place penne in the casserole dish. Pour 2 cups marinara sauce over the pasta. Add chicken bone broth and gently stir to combine.
Sprinkle in half of the spinach (if using), Italian seasoning, salt, and pepper. Cover tightly with foil.
Bake in the preheated oven until pasta is tender and most liquid is absorbed, 25 to 30 minutes.
Remove casserole from oven. Stir in remaining spinach until wilted. Arrange frozen chicken tenders evenly on top of the pasta. Spoon remaining sauce over chicken, just enough to cover lightly. Sprinkle mozzarella and Parmesan evenly over the top.
Bake casserole until chicken tenders reach at least 165 degrees F (74 degrees C) and cheese is bubbly and golden, 15 to 20 minutes. Let the casserole sit 5 minutes before serving so it sets slightly.
