On large platter, season shrimp with salt and pepper. Put to one side. Heat margarine and oil in a heavy black skillet or Dutch oven over medium heat. When margarine is melted, add onions, bell pepper, oregano and garlic. Saute, turning until onion is clear. Add milk and heat until mixture reaches boiling Point. Turn heat down and simmer for about 10 minutes, stirring occasionally. Add shrimp and cook slowly for about 5 minutes, stirring occasionally. Add onion tops, mushrooms and cornstarch. Add corn starch dissolved in mushroom liquid, a little at a time, until sauce is consistency of fairly thick crearn soup. Cook, stirring another 5 minutes, adjust seasonings. Let sit a few minutes, stirring occasionally. Grate Monterey Jack cheese and set to one side. When ready to serve return sauce to burner and bring to boiling point. Mix with spaghetti.
Cajun Country -- New Iberia, Louisiana