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