Preheat the oven to 425 degrees F. Poke holes in all of the potatoes with a fork. Brush the potatoes with 2 tablespoons of olive oil and sprinkle with 1/2 teaspoon each of salt and pepper. Place them on a baking sheet.
On another baking sheet, place the cauliflower and broccoli. Toss it with the remaining olive oil, salt and pepper. Sprinkle with the garlic powder.
Roast both the potatoes and the veggies for about 20 to 25 minutes. Check the veggies – they might be done (totally depends on how roasted you like yours. I like mine VERY roasted.) Roast the potatoes for 15 to 20 minutes more, until fork tender.
Remove the potatoes and cut them down the center. To serve, spoon some of the cheese sauce into the potato, then top with the cauliflower and broccoli. Pour more of the cheese sauce on top and sprinkle with scallions. Top with some freshly cracked black pepper or crushed red pepper. Serve immediately.