Cook pasta shells according to package directions. Rinse in cold water; drain.
Spray a medium skillet with nonstick spray coating. Add mushrooms and onion; cook until tender. Stir in parsley, Italian seasoning, and paprika. Cool slightly.
Mash the tofu in a bowl. Stir in egg white, Parmesan cheese, and mushroom and onion mixture. Stuff each manicotti shell with about 1/4 cup of the tofu mixture. Arrange stuffed shells in a 12x7-1/2x2-inch baking dish.
For sauce, in a medium saucepan combine milk, flour, garlic powder, salt, and pepper. Cook and stir until thickened and bubbly. Pour sauce over pasta in baking dish.
Bake, covered, in a 350 degree F. oven for 20 to 25 minutes or until heated through. Sprinkle with cheddar cheese. Bake, uncovered, 2 minutes more or until cheese is melted. Makes 4 servings.