Clean and slice large white mushrooms into 1/2-inch slices.

Cut white parts of green onions into 1/2-inch pieces and chop the green parts, setting aside 1/4 cup.

Deseed and cut green peppers into 1 1/2-inch squares.

Soak bamboo skewers in water for at least an hour.

Alternately thread mushroom slices, green onion pieces, and green pepper squares onto the soaked skewers.

Arrange threaded skewers in a single layer in a flat dish.

In a separate bowl, mix together soy sauce, sugar, sesame oil, finely chopped garlic cloves, 1 tablespoon of toasted sesame seeds, and black pepper to create the marinade.

Pour the prepared marinade over the skewered mushrooms and vegetables, ensuring both sides are well coated.

Cover the dish and refrigerate for a minimum of 30 minutes and up to 2 hours, turning the skewers once during marination to ensure even flavor absorption.

Preheat grill or broiler to high heat.

Grill or broil the skewers, brushing them with the remaining marinade during cooking.

Cook for approximately 3-5 minutes per side, until browned and cooked through.

Just before serving, sprinkle the remaining toasted sesame seeds and chopped green onions over the kebabs.

Serve hot.