In a large pot over medium-low heat, make a roux with flour and oil. Cook stirring constantly, until golden brown and smooth, at least 20 minutes, preferably longer. Add onions and garlic and cook until almost soft. Add 1-1/2 cups cold water and simmer 30 minutes. Add crawfish and cook about 10 minutes. (note: if using chicken or sausage, cook ingredients longer to ensure they'll be done when rice is done.) Add 2 more cups of water and bring to a boil. Add remaining ingredients, stir to blend, but not too much. Reduce heat to low, cover pot, and cook about 30 minutes or until rice is cooked. Try not to open lid during final cooking. Fluff rice thoroughly with fork before serving.