Cook the elbow macaroni according to package instructions until al dente. Drain and set aside.
In a medium saucepan, melt the butter over medium heat. Whisk in the flour and cook for about 1 minute until lightly golden.
Gradually whisk in the whole milk, stirring constantly until the mixture thickens, about 3-5 minutes.
Remove the saucepan from heat and stir in the Cheddar cheese, Gruyère cheese, Dijon mustard, garlic powder, salt, and black pepper until the cheese is melted and the sauce is smooth.
Gently fold the cooked macaroni and chopped lobster meat into the cheese sauce until well combined.
Preheat the oven to 350°F (175°C). Transfer the lobster mac and cheese into a greased 2-quart baking dish.
In a small bowl, mix the breadcrumbs with a little melted butter (optional) and sprinkle them evenly over the top of the mac and cheese.
Bake in the preheated oven for 20 minutes. For an extra crispy topping, broil for an additional 2-3 minutes, keeping a close eye to prevent burning.
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley before serving.