Preheat grill to 350 degrees F.
Quarter red and green pepper, then place them on the grill, cooking until tender. Once grill marks are formed, remove peppers from grill and set aside. Boil elbow macaroni in salted boiling water until al dente - drain and set aside. In a large saucepan over medium heat, melt butter and then whisk in flour to thicken, about 1 minute. Add 1 cup milk and whisk in. Begin adding cheeses 1 at a time, thoroughly whisking each cheese. If sauce becomes too thick, add remaining cup of milk. Once all cheeses are blended add salt, black pepper, cayenne pepper, grilled peppers, jalapeno pepper and stir to combine. Add elbows to mixture and stir again. Once combined well, add to a cast iron 9 by 13-inch rectangle casserole dish, and sprinkle top with bread crumbs and an additional 1/2 teaspoon cayenne pepper. Place on grill for 12 minutes. Let stand a few minutes before serving.