Place ground turkey in a bowl, sprinkle with salt, pepper, garlic powder, dry mustard, and oats. Pour over beaten egg and grate cold butter over the top.
Carefully mix the meatballs. Use your fingers to mix and fold to keep oats and butter evenly dispersed. Cover and place in fridge.
Preheat oven to 350°F. Add all the glaze ingredients into a medium saucepan and place over medium heat. Bring to a simmer, and let cook 20 minutes stirring occasionally. Use the back of your spoon to ensure berries are broken down.
While glaze is cooking, portion 15 meatballs into a medium casserole dish. The meatballs should be touching or close together. Place in preheated oven and bake for 20 minutes.
While meatballs are baking, return to the glaze. When it's cooked down and thickened to a syrup that coats the spoon thickly, strain through a fine mesh sieve to remove the seeds. Should yield between 1 to 1 1/4 cups.
After 20 minutes, remove meatballs from oven and pour over strained glaze. Return to oven for 10 to 15 minutes, until meatballs are cooked through to 170°F (will continue to cook for a few minutes out of the oven).
Remove from oven and carefully spoon sauce from bottom of pan over the top of meatballs. Serve immediately.
*If using frozen berries, reduce soy sauce by one tablespoon until tasting combined sauce and add if needed. Also can add cornstarch slurry of 1 tsp and 2 tsp water if it doesn't thicken.