Preheat oven to 425°F. Coat a large sauce pan with olive oil over medium heat. Add onion and cook for about 7 minutes or until translucent, stirring frequently. Add garlic and crushed red pepper and cook for another 2 minutes. Set aside and let cool.
In a large bowl, combine the ground turkey, egg, Parmesan cheese, breadcrumbs, milk and parsley. Squish the mixture with your hands until mixed. Add the onion mixture and kosher salt and continue mixing with hands. The mixture should be fairly wet.
Use wet hands or an ice cream scoop to shape the meatballs to desired size, usually golf ball size. Put some parchment paper on a baking sheet and place meatballs in single layer. Bake for about 15 to 20 minutes or until meatballs start to brown on top. If using right away, add to a simmering marinara sauce for the last 30 minutes. If not using, you can freeze.