Preheat oven to 350F. Line a rimmed baking sheet with parchment paper or aluminum foil.
In a large mixing bowl, combine Italian turkey sausage, mushrooms, onions, roasted red peppers, black olives, Italian seasoning, salt, and black pepper until well combined. Take heaping tablespoonfuls and shape into balls.
Heat 1 tsp avocado oil in a large skillet over medium-high heat. Brown half the meatballs on all sides and transfer to the prepared baking sheet. Heat remaining tsp avocado oil and brown remaining meatballs; transfer to the baking sheet.
Bake about 15 minutes, until a meat thermometer reads 165F in the center of the meatballs.