Combine all ingredients in a bowl and mix gently. Use a cookie scoop or tablespoon scoop to roll into 1 ½-inch balls and place on a lightly oiled rimmed baking sheet.
Transfer sheet to the oven and bake for 18 to 20 minutes until nicely browned, flipping halfway.
For the mushroom marsala sauce
Heat olive oil over high heat. Add the mushrooms and sauté for 5 minutes; add in the arrowroot powder or flour and mix well to coat the mushrooms.
Add in the marsala wine and chicken stock. Add the Greek yogurt and season to taste; stir well and let simmer for an additional 5 minutes.
Divide the mashed potatoes and green beans (if using) into 4 meal prep containers. Place 4 meatballs into each container and spoon over the mushroom marsala sauce.