6 ounces (11/2 cups) whole-grain elbow macaroni, cooked for 3 minutes less than the package directions (about 3 cups cooked)
Nonstick cooking spray
Preheat the oven to 375°F.
Directions
Place the cauliflower into a steamer basket fitted over the pot, cover, and steam until just tender, about 5 minutes. Finely chop the steamed cauliflower.
In a small bowl, combine the bread crumbs, Parmesan, and oil.
In a large saucepan, whisk together the milk and flour until the flour is dissolved. Whisking constantly, bring the mixture to a gentle boil over medium heat. Reduce the heat to medium low and simmer until the mixture thickens slightly, 2 to 3 minutes. Stir in the cheddar, Gruyère, mustard powder, paprika, salt, black pepper, and cayenne pepper. Whisk until the cheeses are melted and the mixture is smooth, 1 to 2 minutes. Add the chopped cauliflower and macaroni and stir until well coated.
Spray an ovenproof 10-inch high-sided skillet with cooking spray. Pour the mixture into the prepared skillet. Sprinkle with the bread crumb mixture, place on a baking sheet, and bake until the top is browned and the cheese is bubbly, 35 to 40 minutes.