In a large (12 inch) skillet over medium-high heat, add 1 tablespoon olive oil. Place the onions in the skillet and cook until softened, about 2 to 3 minutes. Divide the onions in half.

In a large mixing bowl, combine the half of the sauteed onions with the ground turkey, bread crumbs, eggs, 2 tablespoons of the parsley, milk, salt, and black pepper.  Mix until just combined.

Using a 1 tablespoon cookie scoop, portion the meat mixture and roll into balls.

Reheat the skillet over medium-high heat until hot. Add 1 tablespoon olive oil and then part of the meatballs, browning on all sides. It is not necessary to cook the meatballs all the way through. Transfer the meatballs to the slow cooker and continue browning the remaining meatballs in the remaining olive oil until they are all browned.

Whisk together the water, sour cream, flour, tomato paste, bouillon, Worcestershire sauce, and paprika, beating until smooth.

Sprinkle the remaining onion over the meatballs. Top with the mushrooms.

Pour the sauce over the meatballs and mushrooms.

Cover and cook on low for 4 to 6 hours.

Gently toss the meatballs in the gravy. Sprinkle with chopped parsley and serve over egg noodles or mashed potatoes.