Preheat the oven to 350F.
Add 2 tbsp. of butter to a medium cast iron skillet and melt over medium heat. Add the peppers and onions and sauté for about 3 minutes.
Then add the garlic and cook for another minute. Set the veggies aside.
Melt 3 tbsp. of butter in the skillet and add the flour. Make a roux by whisking constantly until it's a golden brown and thickens, about 2-3 minutes.
Pour in the heavy cream and milk. Whisk it together and bring to a simmer to thicken. Add the salt and pepper (season to taste).
Add in the cheddar, mozzarella, and 1/2 cup of the parmesan. Stir until it's fully melted.
Add the cooked veggies back in as well as the Cajun spice, and mix.
Stir in the Lump Crab meat.
Add in the uncooked gnocchi, mix until it's smothered in cheese, and spread the top so the skillet is leveled. Remove it from heat.
To make the panko topping: Put the remaining butter in a small microwave-safe bowl and melt. Add in the panko and mix, then add in the parmesan and mix. Sprinkle the breadcrumb topping evenly over the skillet.
Bake in the oven for 25-30 minutes until the dish is bubbling and the top is golden brown.
Serve immediately and enjoy!