Preheat the oven to 400°F and line a baking sheet with parchment paper

1. Add the ground turkey, bread crumbs, parmesan cheese, egg, parsley, oregano, onion and garlic powder and salt to a bowl. Mix well to combine. 
2. Using about a heaping tablespoon amount, form the turkey mixture into 20 meatballs. Place the meatballs on the prepared baking sheet. Cook on the middle rack for about 10-12 minutes, flipping the meatballs half way through, until the meatballs are cooked through. Remove from the oven and set aside.
3. In the meantime, add the potatoes to a large pot of salted water. Place over high heat and bring to a boil. Cook until the potatoes are tender. Drain. Turn off the burner.
4. Return the potatoes to the pot. Mash the potatoes well. Add the milk and butter and continue to mash until you have well mashed potatoes. Season with salt and pepper. Cover and set aside.
5. To make the picatta sauce. Place a medium skillet over medium-high heat. Add the butter, oil, shallot and garlic. Cook, stirring occasionally for about 3 minutes until just soft and fragrant. 
6. Add the chicken broth and bring to a simmer. Cook for 3 minutes. Stir in the capers, lemon juice and  lemon zest. Continue to simmer.
7. Transfer the meatballs to the skillet along with any juices that have accumulated on the baking sheet. Bring back to a simmer, flipping the meatballs so they get coated with the sauce. 
8. Add the cornstarch to a small bowl and dissolve with about a tablespoon of cold water. Pour the cornstarch into the skillet and stir. Cook until the sauce thickens slightly. 
9. Remove from the heat and add the parsley. 

Serve the meatballs and picatta sauce over a bowl of mashed potatoes.