Pour the pineapple juice from the can into a medium bowl and reserve it for the sauce.
Add the frozen meatballs into a 4-6 quart crock pot.
Scatter the pineapple chunks and diced green pepper over the meatballs.
Combine the saved pineapple juice with brown sugar, vinegar, soy sauce, and cornstarch in the bowl and whisk until smooth.
Drizzle the prepared sauce over the meatballs and cover the crock pot.
Cook everything on low for 2 hours.
Switch the crock pot to high and let it cook for an additional hour to thicken the sauce until it's bubbly around the edges.