Step 1: Combine all the ingredients for the stir fry sauce in a bowl, stirring well until the sugar is fully dissolved. Set aside.

Step 2: Slice a cold piece of sirloin steak into small, bite-sized strips and set aside.

Step 3: Blanche broccoli florets in hot water for a few minutes until they are partially cooked. Drain and set aside.

Step 4: Chop the onion and mince the garlic. Sauté them in a skillet over medium heat until fragrant and translucent.

Step 5: Add the sliced sirloin steak to the skillet and cook for about 2 to 3 minutes on each side, stirring occasionally to ensure even cooking.

Step 6: Add the sliced yellow bell pepper and blanched broccoli florets to the skillet. Stir well to combine with the meat and onions.

Step 7: Pour in the stir fry sauce and cook, stirring frequently, until the sauce thickens and coats the meat and vegetables evenly. Adjust seasoning to taste if needed.