Preheat oven to 400F. Lightly grease a 9×13 baking dish and arrange pepper halves in a single layer in pan.
In a medium bowl, combine both cheeses. Set aside.
In a medium pot or Dutch oven over medium heat, melt 2 tablespoons butter. Add garlic and cook 1 minute until fragrant. Whisk in flour until smooth and let cook 2-3 minutes until golden brown. Slowly drizzle in milk and cream, whisking constantly until smooth and incorporated.
Cook sauce over medium heat, stirring occasionally until sauce is bubbly and thickened. Remove from heat and add 1-1/2 cups cheese mixture, stirring until cheese is melted. Fold cooked pasta into sauce and season with salt and pepper to taste. Set aside for a moment.
In a small bowl, combine breadcrumbs and remaining 1 tablespoon melted butter. Season breadcrumbs with salt and pepper to taste. Set aside for a moment.
Divide mac and cheese mixture between pepper halves. Top with remaining 1-1/2 cups cheese and breadcrumb mixture.
Bake peppers at 400F 20-25 minutes until peppers are tender and cheese is melted. Top with fresh parsley and serve warm. Enjoy!