Make the panade: In a large bowl, stir breadcrumbs and milk.
Let sit 2–3 minutes to hydrate. This keeps the turkey juicy.
Mix the meatballs: Add ground turkey, egg, minced garlic, grated onion, soy sauce, salt, pepper, and garlic powder. Gently mix with a fork or your hands until just combined. Do not overmix or the meatballs will be tough.
Shape: Scoop into 1 to 1.5-inch balls (about 24–28 meatballs).
Lightly oil your hands to prevent sticking.
Brown the meatballs: Heat olive oil in a large skillet over medium-high. Brown meatballs in batches for 1–2 minutes per side. You’re not cooking through—just getting color.
Transfer to the slow cooker.
Make the sauce: In a bowl, whisk honey, soy sauce, ketchup, vinegar, garlic, ginger, and red pepper flakes. Taste and adjust sweet/salty/acid to your liking.
Slow cook: Pour the sauce over the meatballs. Cover and cook on Low for 3–4 hours or High for 1.5–2 hours, until the meatballs reach an internal temperature of 165°F (74°C).
Thicken (optional): If you want a stickier glaze, whisk cornstarch with water.
Stir into the slow cooker during the last 15 minutes. Sauce will thicken as it simmers and cools.
Finish and serve: Gently toss meatballs in the sauce. Sprinkle with green onions and sesame seeds.
Serve over rice with vegetables or set out with toothpicks for an appetizer.