While the beef is cooking, whisk together the soy sauce, water, corn starch, brown sugar, ginger, garlic, chili paste, and red pepper flakes.
1/2 cup low-sodium soy sauce, 1 tablespoon cornstarch, 1/2 teaspoon brown sugar, 2 cloves garlic, 1/2 tablespoon minced fresh ginger, 1 - 2 teaspoons chili paste, 1/4 teaspoon red pepper flakes, 1/3 cup water