Whisk soy sauce, garlic, ginger, scallions, sugar, sesame oil, and black pepper to taste in a medium bowl. Use marinade immediately or refrigerate for up to 2 days.
Shopsmart: Not all soy sauces are the same. Some are saltier, others sweet and thick. Light soy sauces are salty; the "light" refers to the body of the sauce. Dark soy sauces are sweeter and thicker. For the best results with this marinade, choose a dark Japanese or Korean soy sauce.
Yield: about 1 1/2 cups