Preheat oven to 450F degrees. Spray inside of 2-quart cast iron Dutch oven and lid with olive oil or canola oil spray.
Scrub potato well and cut out any bad spots or eyes. Cube potato into 1″ cubes. Halve beans or leave whole, as desired.
Line base of pot with onions. Wash fish and pat dry with paper towels. Lay the fish over the onions in the bottom of the pot. Sprinkle the top side liberally with Cajun seasoning mix according to taste. Layer potatoes, garlic, onions, green beans, and tomatoes, interspersing sprinkles of spices as desired. Pack in as many vegetables as possible while still able to get a clean seal for the lid.
Cover and bake for 35-45 minutes, or until fish flakes easily. You should smell the aroma wafting from the oven that tells you everything is done.
Use cajun or creole seasoning to bring that “blackened” taste to fish, seafood, poultry, and meat, too.
Check out Tony Chachere’s Original (creole) Seasoning, but in a pinch, any cajun seasoning mix from the grocery will do, or mix together paprika, salt, and a dash of cayenne to make your own. Careful with the cayenne as a little goes a long way.
Frozen green beans are an easy solution when you’re looking for something green to toss into a pot meal. Use 1-2 cups, reseal the baggie and keep it in the freezer — a single bag can stretch over quite a few meals.