Originally this was suggested for tuna. I've not tried it with tuna but it's great on shish-kabob! I also marinade the vegetables.

1/4 cup soy sauce
2 tbsp. lemon juice
1 tbsp. brown sugar
2 cloves garlic, finely chopped
1 tbsp fresh grated ginger
2 tbsp. chopped green onion
2 tbsp. sesame oil
1/2 teaspoon of hotsauce
pinch of fresh ground pepper