Melt butter in a Dutch oven or other large heavy pot, add the onions and bell peppers.
Sauté over medium high heat.
Brown well (being sure to scrape the bottom of the pot frequently to loosen any stuck particles) (You want to caramelize the onions to bring out their sweetness) (This process will take about 45 minutes).
Reduce the heat to medium low, add the salt, peppers, crawfish fat, and water.
Stir well and let simmer 30 minutes more (you can prepare the dish in advance to this point; about 30 minutes before serving).
Reheat the mixture over medium heat.
Raise the heat to medium high, stir in the crawfish and cook for 10 minutes.
Add the green onions and parsley and let cook for another 5 minutes.
Place generous servings of hot cooked rice in the middle of large flat plates and spoon the crawfish all around.