In a heavy-bottomed pot, make a medium brown roux with the oil and flour. Add tomato sauce, Ro-Tel and brown sugar. Simmer about 15 minutes. Add onions, green onions, bell peppers, parsley, mushrooms, and garlic. Simmer about 15 minutes.
Add about 4 cups of water and salt and pepper. Cook for 2 hours, adding water as necessary.
Add shrimp. Cook 20-25 minutes.
Serve over rice.