Preheat oven to 375°F and grease a cast iron skillet or baking pan until lightly coated. The pan should be ready for a slight sizzle when batter hits it.
Melt butter in a pan over medium heat, then add onions and bell peppers. Cook for 3–5 minutes until soft and fragrant.
In a large bowl, whisk eggs, milk, melted butter, salt, pepper, garlic powder, and Cajun seasoning until smooth and creamy.
Stir in Jiffy cornbread mix gently until just combined. The batter should be thick but still pourable.
Fold in crawfish tails, cooked vegetables, green onions, and shredded cheese. Mix slowly to keep texture light.
Pour batter into prepared pan and spread evenly. Tap lightly to remove air pockets.
Bake for 45–55 minutes until golden brown on top and firm in the center. The edges should pull slightly from the pan.
Let rest for 10 minutes before slicing so it sets properly and holds shape.