In a medium bowl, combine mirin, minced garlic, grated ginger, and sesame oil. Add cubed sirloin steak, ensuring it's well coated with the marinade. Cover and let marinate for at least 30 minutes.

Heat a large skillet over medium-high heat and add a drizzle of sesame oil. Toss in sliced carrots, zucchini, and mushrooms. Sauté for 5-7 minutes until tender.

Push the sautéed vegetables to one side and add the marinated steak. Cook for about 5-7 minutes until desired doneness is reached.

If using pre-cooked fried rice, heat it separately over medium heat until warmed. For plain rice, simmer it with soy sauce and sesame oil.

Assemble bowls with rice at the bottom, topped with sautéed vegetables and juicy steak for a colorful presentation.