Maui Sweet & Sour Beef

1 1/2 lbs boneless beef sirloin, cut in 1 1/2" pieces
1/3 cup brown sugar, packed
1/3 cup cider vinegar
1 small can pineapple chunks (drain and reserve juice)
3 tablespoons soy sauce
1 clove minced garlic
3 tbsp oil
1/2 teaspoon dried red pepper flakes
3 cups baby carrots, cut lengthwise
1 large green pepper, chopped
1 large onion, cut into 1/4s and separated
3 tbsp cornstarch
3 tbsp cold water

Combine sugar, vinegar, reserved pineapple juice, soy sauce and minced garlic in a small bowl. Add brown sugar, stirring until the sugar is completely disolved into the sauce (a couple of minutes).

Season pieces of beef with salt and pepper to taste. Heat cooking oil in frypan and brown beef & red pepper flakes together, then add to slow cooker. Then add carrots and onion pieces. Then pour sauce over, cover and cook on low 7-9 hours or high for 3-4 hours.

Change slow cooker setting to high, if it isn't already. In a small bowl, whisk cornstarch and water together. Pour cornstarch into slow cooker, then add pineapple chunks and green pepper. Stir quickly to combine, cover and continue cooking for half an hour or until sauce is thickened. Serve over rice.