Gather all ingredients.

Combine 3 tablespoons soy sauce, olive oil, 1 clove minced garlic, red pepper flakes, salt, and black pepper in a shallow dish. Add pork; toss to evenly coat. Cover the dish with plastic wrap. Marinate in the refrigerator for 3 hours.

Combine beef broth, cornstarch, remaining 2 tablespoons soy sauce, brown sugar, remaining 2 cloves minced garlic, and ginger in a small saucepan; bring to a boil, stirring constantly. Reduce heat; simmer sauce for 5 minutes. Set aside.

Preheat an outdoor grill for high heat and lightly oil the grate. Remove pork from marinade and shake off excess; discard marinade. Thread pork onto skewers, alternating with mushrooms, onion, tomatoes, and pineapple.

Cook on the preheated grill, flipping skewers every few minutes and basting with sauce often, until pork is cooked through, about 15 minutes. An instant-read thermometer inserted into pork centers should read at least 145 degrees F (63 degrees C).