1.In a large bowl, combine turkey, breadcrumbs, onions, egg, salt, dried oregano, dried basil, garlic powder, pepper, 1/4 cup parsley, and 1/4 cup parmesan. Mix just until distributed. Shape meat mixture into small meatballs.
2.In the Instant Pot, add half of the marinara sauce. Arrange meatballs on the sauce and then top with the remaining sauce.
3.Secure lid and move pressure release valve to the SEALING position. Press Manual and cook at high pressure for 8 minutes.
4.When cooking is complete, press CANCEL and use QUICK release. Mix in 1/4 cup chopped parsley. Serve hot over spaghetti and garnish with remaining parmesan cheese.