In a small bowl, soak bread in broth or milk. Tear with your hands until it resembles a soft paste.
In a large bowl, combine ground beef, soaked bread, onions, egg, 1 teaspoon salt, and 1/4 teaspoon pepper. Gently mix until combined.
Using a small scoop, portion about 1 tablespoon of meat mixture and using roll between palms of hands into a 1-inch diameter ball.
Arrange meatballs in a single layer on a parchment-lined baking sheet and freeze for about 20 to 30 minutes or until firm.
In a bowl, combine pineapple juice, rice vinegar, ketchup, brown sugar, 1 teaspoon of salt. Stir until well-blended and set aside.
In a wide pan over medium heat, heat about 1 tablespoon canola oil. Add bell peppers and cook for about 30 to 40 seconds. Remove from pan and keep warm.
Add pineapple chunks and cook for about 20 to 30 seconds. Remove from pan and keep warm.
In the pan, add another 1 tablespoon oil if needed. Add meatballs in a single layer and cook for about 1 to 2 minutes on each side or just until lightly browned. Remove from pan and drain on paper towels. Keep warm.
Remove excess oil from the pan except for about 1 tablespoon. Add onions and cook until softened.
Add pineapple mixture and bring to a boil.
Add browned meatballs in a single layer. Lower heat, cover, and cook for about 8 to 10 minutes or until meatballs are fully cooked.
In a bowl, combine 1/4 cup water and cornstarch and stir until smooth. Add to pan, whisking to prevent lumps. Season with salt and pepper to taste. Cook for about 2 to 3 minutes or until thickened.
Add bell peppers and pineapple chunks. Continue to cook for about 1 to 2 minutes or until heated through. Serve hot.