Mix the egg and 1/4 cup polenta in a large bowl; let sit 5 minutes. Add the turkey, ricotta, 2 tablespoons each parmesan and parsley, the chopped garlic, 1/2 teaspoon salt and a few grinds of pepper; mix with your hands until combined. Form into eight 1 1/2-inch meatballs.
Heat the olive oil in a large nonstick skillet over medium-high heat. Add the meatballs and cook, turning, until lightly browned, about 5 minutes. Transfer to a plate. Add the sliced garlic to the skillet and cook, stirring, until slightly softened, about 1 minute. Add the tomatoes and red pepper flakes and bring to a boil. Reduce the heat to medium and return the meatballs to the skillet. Simmer, stirring occasionally, until the meatballs are cooked through, about 10 minutes. Stir in the remaining 2 tablespoons parsley and season with ¼ teaspoon salt and a few grinds of pepper.
Meanwhile, bring 4 cups salted water to a boil. Reduce the heat to medium low and add the remaining 3/4 cup polenta. Cook, stirring constantly, until the water is absorbed and the polenta is soft and creamy, 7 to 8 minutes. Stir in the remaining 1/4 cup parmesan and season with salt and pepper. Top each serving of polenta with the meatballs and sauce.