In a large bowl, combine the shrimp, salt, pepper, and red pepper flakes. Blend well. Cover and place in the refrigerator.
In a large pot over medium heat, melt 1/2 cup of margarine and add the onions. Saute the onions until they are translucent.
Stir in the celery and bell pepper. Increase the heat to high and stir occasionally for 20 minutes. Add the remaining 1/2 cup of margarine and bring to a boil. Fold in the shrimp and reduce heat to medium cook for 10 minutes.
Mix the cornstarch and water together and slowly pour it into the pot; just covering the top of the shrimp mixture. Cook on medium/high heat until the celery is soft; about 20 minutes. Add any additional salt, pepper and red pepper flakes to taste.