In a medium mixing bowl combine the sliced beef, minced garlic, 2 tablespoons sesame oil, 1 tablespoon cornstarch, 1 tablespoon low-sodium soy sauce, 1 tablespoon water, 1 teaspoon dark brown sugar, grated ginger, 1/2 teaspoon baking soda, and 1/2 teaspoon crushed red pepper flakes; stir to coat the beef, cover, and refrigerate for at least 4 hours or up to 24 hours.
While the beef marinates, prepare the sauce by whisking together 1/2 cup low-sodium soy sauce, 2 tablespoons brown sugar, and 2 tablespoons all-purpose flour in a small bowl; set aside.
When ready to cook, heat a 12-inch high-sided skillet over medium-high heat and add 1 tablespoon sesame oil (or vegetable oil); swirl to coat.
Add the marinated beef along with its marinade and half of the prepared sauce to the hot skillet; cook, stirring occasionally, about 5 minutes until the beef is no longer pink.
While the beef cooks, steam the frozen vegetable mix according to package directions until just heated through.
Stir the remaining sauce into the skillet with the cooked beef, add the steamed vegetables, and cook about 3 minutes more, stirring, until the sauce thickens and coats the meat and vegetables.
Remove from heat and serve the beef and vegetables over 4 cups of cooked white or brown rice.