In a large liquid measuring cup, combine soy sauce, brown sugar, rice vinegar, sesame oil, ginger, garlic powder, and red pepper flakes, if using. Whisk until smooth.
½ cup low-sodium soy sauce, ⅓ cup packed light brown sugar, 2 Tablespoons rice vinegar, 1 Tablespoon toasted sesame oil, ¾ teaspoon ground ginger, ½ teaspoon garlic powder, ⅛ teaspoon red pepper flakes
Place the cut beef in a prep bowl and pour about half of the soy sauce mixture on top. Set aside to marinate for at least 20 minutes, or cover and marinate in the fridge for up to 24 hours. Cover and reserve the other half of the soy sauce mixture in the fridge, also, if marinating the beef for a long time.
1 pound sirloin tips
When ready to cook, heat the oven to 450°F. Remove beef from the fridge, if it was chilled, and line a large rimmed sheet pan with parchment paper or a silicone mat.
Spread the broccoli out on the sheet pan. Drizzle lightly with olive oil and sprinkle with salt and pepper. Roast for 8 minutes.
2-3 cups broccoli florets, extra-virgin olive oil, kosher salt and black pepper
After 8 minutes, add sliced pepper to the pan and toss together with the broccoli. Push the veggies to one side, then add steak to the other side. Discard the marinade left in the bowl.
1 bell pepper
Return everything to the oven and roast for another 8-10 minutes, or until the veggies are tender-crisp and the beef is cooked through to 145°F.
Place the reserved soy sauce mixture (not what the beef was in) in a small saucepan over medium-high heat. Bring to a boil, then reduce heat to medium and let it bubble for 1-2 minutes.
While the sauce is simmering, mix the cornstarch and cool water in a small bowl and stir into a thin slurry, then stir this into the soy sauce mixture. Keep bubbling until the sauce is thick enough to visibly coat the back of a spoon. Remove from the heat and set aside until ready to serve.
1 teaspoon cornstarch plus 1 teaspoon cool water
Remove sheet pan from the oven and toss everything together. Serve right away, over rice if you like, drizzled with extra sauce and topped with green onions and sesame seeds.
rice, green onions, and sesame seeds