Preheat the oven to 450°.

Spray a rimmed baking tray with nonstick cooking spray, pile the cauliflower florets on, drizzle with two tablespoons of the oil, and sprinkle with one teaspoon of the Cajun or Creole seasoning. Toss and distribute the cauliflower evenly across the pan.

Place in the oven and roast for 10 minutes, stir, and continue roasting for five minutes longer. Set aside.

Heat 1/4 cup of the oil in a two-quart (or larger) pot and set over medium-high heat. When the oil starts to shimmer, add the holy trinity (celery, green bell peppers, and onions).

Sauté for about five minutes, until the vegetables are soft, then lower the heat to medium and sprinkle in the remaining Cajun or Creole seasoning and the flour. Stir well, evenly distributing the seasoning and flour. Cook for just a minute, as the pot will become dry.

Add the tomatoes and their juice and the water into the pot and stir well to scrape up the cooked-on bits from the bottom of the pan.

Raise the heat to medium-high and bring the étouffée to a strong simmer, uncovered, then stir, lower the heat to medium, and simmer gently for 20 minutes.

After 20 minutes, add in the roasted cauliflower, stir well, and serve with the green onions and long-grain rice.