In a medium bowl, whisk together mirin, minced garlic, ginger, sesame oil, and soy sauce. Place the sirloin steak into the marinade, ensuring it's fully coated. Cover the bowl and let it marinate in the refrigerator for at least 30 minutes.

While the steak is marinating, prepare the fried rice according to package instructions. If using leftover rice, heat it in a skillet over medium heat with a splash of soy sauce, stirring continuously for about 5–7 minutes.

Heat a large skillet over medium-high heat and add a tablespoon of sesame oil. Once hot, add sliced carrots, zucchini, and mushrooms, sautéing for about 5-7 minutes until tender.

Remove the marinated steak from the bowl and cook in the same skillet for about 4-5 minutes on each side, or until desired doneness. Let the steak rest for a few minutes before slicing.

In serving bowls, create a base layer of fried rice, place sliced steak on top, add sautéed vegetables, and drizzle with soy sauce.