Preheat oven to 400 degrees F. Line a baking sheet with parchment paper, grease with cooking spray, and set aside.
In a large bowl, combine the turkey, egg, Italian seasoning, 1/2 teaspoon salt, 1/2 teaspoon black pepper, pepper flakes, bread crumbs, parmesan and parsley until evenly incorporated. Form into balls about the size of a golf ball and place on one side of the baking sheet.
Scatter the tomatoes around the meatballs.
Place the potatoes, in a single layer, on the other side of the baking sheet. Drizzle everything with olive oil and season the potatoes with the remaining salt and pepper.
Roast in the oven for about 20 minutes, or until the potatoes are soft enough to smash. Give them a gently push down with a potato masher. Then drizzle with a bit more olive oil and sprinkle with chopped rosemary. Return to oven for another 10 minutes.
Remove once more and top the meatballs and tomatoes with the cheese. Place under the broiler until melted through, about a minute. Top with basil and serve.