In a shallow dish, mix together 3 tablespoons of soy sauce, 1 clove of the mixed garlic, the olive oil and red pepper flakes.
Add the pork cubes to mixture, coat evenly, cover the dish and let marinade in the fridge for 3 hours.
In a saucepan, combine beef broth, cornstarch, the other 2 tablespoons of soy sauce, brown sugar, the rest of the minced garlic and the ginger. Bring to a boil while stirring often. Reduce heat and simmer for 5 minutes.
Preheat an outdoor grill to high heat and lightly oil grate. Thread pork pieces on skewers, alternating veggies and pineapple. Cook on grill for 15 minutes or until meat is finished. Rotate skewers for even cooking, and baste often with sauce while grilling.