In a medium bowl, combine mirin, minced garlic, grated ginger, and sesame oil to create a flavorful marinade. Add diced sirloin steak, ensuring each piece is thoroughly coated. Cover and refrigerate for at least 30 minutes or up to 24 hours.

While the steak marinates, wash and chop your vegetables. Slice the carrots and zucchini thinly for even cooking, and quarter the mushrooms to enhance their texture.

Heat a large skillet over medium heat and drizzle in some oil. Once shimmering, add the prepared vegetables. Sauté for about 5 to 7 minutes until tender and vibrant.

Increase heat to medium-high and add the marinated steak to the skillet with the vegetables. Sear for about 4 to 5 minutes, turning occasionally.

Once cooked, remove from heat and gently mix the sautéed vegetables with the beef. Serve over fried rice and drizzle with soy sauce.