Sauté onion, green onions, chili peppers, and bell peppers in margarine for about 10 minutes. Season with salt, black pepper, cayenne pepper, oregano and garlic. Add whipping cream. Bring to a boil, reduce heat, and simmer for 10 minutes. Stir in sour cream and whisk for about 3 minutes. Add 1½ cups Monterey Jack cheese and stir until melted. Set aside. Sauté shrimp or crawfish for about 6 minutes or until done.

Spoon about ½ cup of the sauce in the bottom of a 9x13-inch baking dish. Divide shrimp or crawfish down the center of each tortilla and spoon a little sauce over the top; wrap each tightly and place, seam-side down, in prepared pan. Spoon remaining sauce over enchiladas and sprinkle with remaining cheese. Bake at 350ºF for 25 to 30 minutes until browned and bubbly.