Cook the manicotti shells according to package directions. Drain shells; rinse with cold water. Drain again.
For sauce, in a medium saucepan cook the onion and garlic in the margarine or butter until onion is tender. Stir in flour, bouillon granules, paprika, red pepper, and black pepper. Add milk all at once. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more. Gradually add cheese, stirring until melted. Remove from heat.
In a large skillet cook the ground beef or pork until brown. Drain fat. Stir in peas, walnuts, 2 tablespoons pimiento, and 1 cup of the sauce. Fill each manicotti with about 1/4 cup of the meat mixture. Arrange manicotti in six individual au gratin dishes or in a 3-quart rectangular baking dish. Pour the remaining sauce over the filled manicotti. Cover manicotti with foil.
Bake in a 350 degree F. oven about 20 minutes for individual dishes or about 35 minutes for the baking dish or until heated through. If desired, sprinkle with sliced green onion and additional diced pimiento. Makes 6 main-dish servings.