Heat the oven to 425°F and oil a rimmed sheet. Mix panko and milk, then fold in pork, egg, water chestnuts, scallions, ginger, salt and pepper just until combined. Shape 24 equal meatballs.
Bake for 16 to 20 minutes until the centers reach 160°F. Meanwhile, simmer broth, honey, soy sauce, vinegar and garlic in a saucepan for 2 minutes.
Transfer hot sauce and hot meatballs to a 4-quart slow cooker. Cover and cook on HIGH for 2 hours, turning gently through the sauce once after 1 hour.
Whisk cornstarch with slurry water and fold into the sauce. Cover and cook on HIGH for 15 to 20 minutes until glossy and thick enough to coat a spoon; confirm the meatball centers reach 165°F.
Turn gently to coat and serve about 3 meatballs per appetizer portion. Hold on WARM only while the food stays at least 140°F, keeping the lid on between servings.