Heat the oven to 425°F and line an 18-by-13-inch rimmed sheet pan with parchment rated for that temperature. Toss squash and onion with 1 tablespoon oil and 1/4 teaspoon salt and roast for 18 minutes.
Mix turkey, ricotta, breadcrumbs, egg, Parmesan, herbs, garlic, pepper and remaining salt gently in a bowl. Form 16 equal meatballs with lightly damp hands.
Turn the vegetables and move them toward the edges. Arrange meatballs in the open spaces and brush lightly with remaining oil.
Roast for 18 to 22 minutes until the centers of the meatballs reach 165°F and squash is tender with browned corners.
Drizzle balsamic vinegar over the vegetables and turn them gently. Serve 4 meatballs with one-quarter of the squash and onion per portion.