Heat the oven to 400°F. Line a rimmed baking sheet with parchment paper.
In a large bowl, combine the ground turkey, egg, breadcrumbs, Parmesan, onion, Italian seasoning, garlic powder, salt, black pepper, and 2 tablespoons of the marinara. Mix gently until everything is just combined.
Shape the mixture into a compact loaf in the center of the prepared baking sheet. Avoid packing it too firmly, which can make the meatloaf dense.
Toss the zucchini and red bell pepper with the olive oil. Arrange the vegetables around the meatloaf in a single layer.
Bake until the meatloaf reaches 165°F in the center and the vegetables are tender, about 35 to 45 minutes. Spread the remaining marinara over the top of the loaf during the final 10 minutes of baking.
Let the meatloaf rest for 5 minutes before slicing. Serve with the roasted vegetables.