Preheat oven to 425 degrees Fahrenheit.

In a 9 x 12 glass baking dish, place the diced plum tomatoes, bell peppers, onion, and andouille sausage. Drizzle one tablespoon of the olive oil and sprinkle one teaspoon of the cajun seasoning on top. Mix well and then push to the sides of the dish leaving a large hole for the mahi mahi.

Drizzle one tablespoon of olive oil on the empty spot in the baking dish. Then add the large frozen mahi mahi filet to the dish (skin side down). Drizzle the remaining one tablespoon of olive oil on top and sprinkle the remaining one teaspoon of cajun seasoning on top of the fish.

Place aluminum foil on top of the glass baking dish and bake for 25 minutes. Then remove the aluminum foil from the dish and bake for an additional 15 minutes until internal temperature reads 165 degrees Fahrenheit. Remove from the oven, carefully cut the fish in 3-4 pieces depending on the size of the filet. Place fish on plates and top with tomato, pepper, sausage mixture. Enjoy immediately.