In a medium bowl, combine the ground chuck, breadcrumbs, milk, beaten egg, 1 teaspoon Italian seasoning, 1/2 teaspoon dried parsley, 1/4 teaspoon red chili flakes, 1/2 teaspoon onion powder, 1/4 teaspoon granulated garlic, 1 teaspoon salt, and 1/2 teaspoon ground black pepper; mix gently until just combined. Cover and refrigerate for at least 30 minutes.
While the meat chills, heat 2 tablespoons olive oil in a large pot or Dutch oven over medium heat. Add the thick-sliced garlic and cook until soft and fragrant, about 1–2 minutes, then remove and discard the garlic slices.
Add the canned tomato puree and diced tomatoes to the pot, then stir in 1 1/2 teaspoons Italian seasoning, 1/2 teaspoon dried basil, 1/4 teaspoon red chili flakes, 2 teaspoons salt, and 1/2 teaspoon ground black pepper. Reduce heat to low, cover, and simmer for 25–30 minutes, stirring occasionally.
Taste the sauce and add up to 1 tablespoon sugar if it tastes too acidic; stir and adjust as needed.
Preheat the oven to 425°F (220°C). Line a rimmed baking sheet with foil and lightly coat with nonstick spray.
Remove the meat mixture from the refrigerator and form into 1½-inch (about 1 tablespoon) meatballs. Place them on the prepared baking sheet, spacing evenly.
Bake the meatballs for 10–15 minutes, until browned and cooked through.
Meanwhile, cook the spaghetti according to the package directions until al dente; drain and divide among plates.
To serve, spoon marinara over the pasta, top with baked meatballs, and sprinkle with grated Parmesan and chopped fresh parsley.
