In a bowl, combine mirin, minced garlic, grated ginger, sesame oil, soy sauce, salt, and pepper. Cut the sirloin steak into bite-sized pieces and coat in the marinade, resting for at least 30 minutes.

Wash and chop carrots, zucchini, and mushrooms. Sauté vegetables in a skillet with sesame oil for 5-7 minutes until tender.

Heat the skillet over medium-high heat and add marinated steak. Cook for 3-4 minutes on each side until seared.

In a separate pan, heat sesame oil and add pre-cooked rice with soy sauce and remaining vegetables. Fry for 5-7 minutes, stirring continuously.

Assemble the bowls with fried rice as the base, followed by sautéed vegetables and slices of steak. Serve immediately.