Preheat oven to 350°F. Spray a 2 1/2 quart casserole dish or 9 x 13-inch baking dish with non-stick spray. Set aside.
Combine 1/4 cup of Parmesan cheese and one teaspoon paprika in a small bowl. Set aside.
Melt butter in a large non-stick skillet over medium heat. Add onions; cook for 5 minutes or until tender. Increase heat to medium-high and add mushrooms. Cook, stirring frequently until mushrooms begin to brown, about 3 minutes.
Sprinkle on flour, salt, pepper and garlic powder. Cook for several minutes. Add milk; stir constantly until thick and bubbly. Add 3/4 cup of Cheddar cheese; stir until melted. Add ham and green peas; stir to combine.
Add undiluted cream of mushroom soup, 1/2 cup of grated Parmesan cheese, sherry and drained pimentos. Stir to combine. Add cooked spaghetti; toss to combine.
Transfer tetrazzini mixture to prepared baking dish. Bake uncovered in preheated 350°F oven for 25 minutes or until heated through and bubbly. Remove from oven and top in diagnol rows of parmesan/paprika mixture, shredded cheddar cheese and toasted almonds. Return to oven for 10 additional minutes or until cheeses are melted.
Yield: 8 servings. (See Tip 5)