Step 1
Bring a large pot of lightly salted water to a boil. Stir in lasagna noodles and return to a boil. Cook the pasta uncovered stirring occasionally until the noodles have cooked through but are still firm to the bite about 8 minutes. Drain and set aside.
Step 2
Preheat oven to 350 degrees F (175 degrees C).
Step 3
Spray a 9x13-inch baking dish with cooking spray.
Step 4
Heat olive oil in a large skillet over medium-high heat. Cook and stir shallots and garlic in the hot oil until shallots are tender and translucent about 5 minutes.
Step 5
Stir red bell pepper and red pepper flakes into the shallot mixture until bell pepper is slightly softened 1 to 2 minutes.
Step 6
Mix mushrooms into the skillet; season with salt and black pepper. Cook and stir until the mushrooms have given up their liquid and are browned about 10 minutes more.
Step 7
Stir ricotta cheese into the mushroom mixture; remove skillet from heat and set aside.
Step 8
Melt butter in another skillet over medium heat. Whisk in flour until smooth 2 to 3 minutes.
Step 9
Whisk milk into flour mixture until smooth; bring to a simmer and whisk constantly until thickened about 5 minutes. Season with salt and black pepper.
Step 9
Coat the bottom of the prepared baking dish with a small amount of the white sauce.