Bring a large pot of water to a boil, season it with salt, and add in your pasta. When pasta is done, drain and set aside.
In the meantime, in a small pot on medium heat, melt the butter and whisk in the flour until there are no large clumps. Pour in the milk and continue whisking until mixture has thickened up. Add the cajun seasoning and cayenne pepper.
Pour in the cheese and whisk together until all has melted and is smooth.
Take the cooked pasta and pour it in a small casserole dish. Take the cheese sauce mixture and pour it all over the top of the pasta. Sprinkle panko breadcrumbs on top.
Put casserole dish in broiler on high and cook until panko has browned and cheese is a bit bubbly.