Preheat the oven to 350 °F and spray an 8x8 baking dish with nonstick spray.
Cook lasagna noodles according to package directions, omitting salt. They'll be done when they're very al dente, but still easy to bend and roll. Use tongs to put them on a plate while you make the rest of the meal.
Heat the olive oil in a skillet and cook the mushrooms, onions, bell pepper and one clove of minced garlic for 5-6 minutes, or until the vegetables are soft. Set aside.
In a bowl, mix together the ricotta cheese, the egg white, dried oregano, dried basil, salt and pepper.
Mix the ricotta cheese mixture and the cooled vegetables together, spread on top of the lasagna noodles and roll them up. Place the rolls seam-side down in the baking dish.
Cover the baking dish tightly with foil and bake for about 25 to 30 minutes, until heated through.
While the noodles bake, make the sauce by whisking the flour into the broth and bringing the mixture to a boil. The flour will thicken the sauce, and adding it to the broth first is critical for avoiding lumps!
Next, add the 2 minced garlic cloves and tomato to the broth and let the mixture simmer for 2 minutes or so, until the sauce thickens.
Slowly stir the skim milk and parmesan cheese into the sauce until the cheese is fully melted and incorporated.
When the lasagna rolls come out of the oven, spoon the sauce over them
