Step 1

Place the cornstarch and water in a small bowl and whisk until completely dissolved. Transfer to a 5-quart or large slow cooker. Add the pineapple juice, vinegar, soy sauce, ketchup, and brown sugar and stir to combine. Add the onion and bell pepper and stir to combine. Cover and turn on to the LOW setting while you make the meatballs.

Step 2

Whisk the egg in a large bowl. Add the breadcrumbs, milk, salt, ginger, and pepper and stir to combine. Add the ground beef, onion, and garlic. Use your fingers to work the mixture together just until all the ingredients are evenly combined. Do not overwork.

Step 3

Scoop out about a tablespoon of the meatball mixture and roll into balls in palm of your hands. Place in the slow cooker. Repeat until all the meatballs have been shaped. The meatballs will not be completely submerged with the sauce. Gently stir and scoop a little sauce over the top so that they're coated.

Step 4

Cover the slow cooker and cook until the meatballs are no longer pink at the center, 3 to 4 hours on the LOW setting. Gently stir, top with the scallions, and serve warm.