Combine first 6 ingredients in a bowl. Heat a large nonstick skillet over medium-high heat. Add soy sauce mixture; cook until lightly thickened, about 1 minute. Add vegetables and red pepper flakes. Cook, stirring constantly, until vegetables are soft, about 1 minute. Add shrimp and 1/4 cup water. Cook, stirring often, until shrimp are just cooked through, 2 to 3 minutes more. Divide among 4 bowls; serve immediately.