Cook patty shells according to package directions. Remove from oven and use a paring knife to scoop center out of each patty shell. Set aside. In a 12-inch, cast iron skillet, melt butter over medium-high heat. Drain crawfish tails in a colander, reserving fat and natural juices. Sauté tails 5–10 minutes or until curled and heated thoroughly but not overcooked. Remove from heat, season with salt, pepper and granulated garlic then set aside. In a large Dutch oven, heat vegetable oil over medium-high heat. Whisk in flour and cook 3–5 minutes or until a dark brown roux is achieved, stirring constantly. Add onions, celery, bell peppers and minced garlic and sauté 3–5 minutes or until vegetables are wilted, stirring occasionally to prevent vegetables from scorching. Pour in tomato sauce and continue cooking 3 minutes. Slowly add water or stock, 1 quart at a time, until a thick stew-like consistency is achieved. Add crawfish fat, reserved drippings and bay leaves, stirring to incorporate. Season to taste with salt, pepper and granulated garlic. Bring to a rolling boil, reduce to simmer and add sautéed crawfish and pan drippings, stirring to combine. Simmer stew approximately 45 minutes, stirring occasionally. Do not boil. Additional water or stock may be needed during the cooking process to retain volume and consistency. Adjust seasonings to taste using salt, pepper and granulated garlic. Add green onions and parsley. Cook 15–20 minutes or until desired richness is achieved, stirring often. Ladle a generous serving of crawfish stew into center of each patty shell. Serve as an appetizer or entrée.