Stir together 3 tbsp.
soy sauce, olive oil, 1 clove garlic (minced).
Season with red pepper flakes, salt, and pepper.
Stir in pork and coat evenly with marinade.
Cover with plastic wrap.
Refrigerate for 3 hours.
Stir together, beef broth, cornstarch, 2 tablespoons soy sauce, brown sugar, 2 cloves, minced garlic and ginger, in a saucepan.
Bring contents to a boil.
Reduce heat and simmer for 5 minutes.
Preheat an outdoor grill for high heat.
Grease grate with oil.
Alternate between adding pork cubes, mushrooms, onion, tomatoes, and pineapple chunks onto skewers.
Place skewers on preheated grill and cook for 15 minutes.
Turn skewers, and brush with sauce.