Stir in the flour to create a roux, cooking for about 1 minute.
Whisk in the milk, continuing to stir until the sauce thickens.
Stir in the garlic powder, onion powder, salt, pepper, and Parmesan cheese, stirring until smooth. Remove from heat.
Preheat the oven to 375°F (190°C).
Spray a 9x13 baking dish with cooking oil.
Spread a thin layer of the white sauce in the bottom of the prepared dish.
Place 3 lasagna noodles on top, followed by half of the ricotta cheese, half of the vegetables, and a third of the white sauce. Repeat the layers with the remaining noodles, ricotta, vegetables, and sauce.
Finish with the last layer of noodles and top with the remaining white sauce.
Add the mozzarella cheese and Italian seasoning on top.
Cover with foil and bake for 25 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.