Add steak, 1 tablespoon soy sauce, rice vinegar, garlic, ginger powder, 1 teaspoon sesame oil, ½ teaspoon black pepper, and ½ teaspoon salt to a large bowl. Set aside to marinate for at least 30 minutes.
Heat 1 teaspoon sesame oil, and 1 teaspoon olive oil in a large skillet over medium-high heat. Add steak and cook for 3 or 4 minutes, until browned with a nice crust. Remove the steak to a plate.
Add 1 teaspoon sesame oil and 1 tablespoon butter to the hot skillet. Add zucchini, carrots, mushrooms, and onions; season with garlic powder and 1 tablespoon soy sauce. Cook the vegetables for 10 minutes, or until tender. Transfer vegetables to a plate. Wipe the skillet clean if needed.
In the same skillet, add remaining 2 tablespoons butter and 1 teaspoon sesame oil over medium-high heat. Add frozen rice and cook for 5 or 6 minutes, stirring occasionally. Toss rice in the remaining tablespoon of soy sauce. Cook for an additional 1 or 2 minutes or until hot.
Evenly divide fried rice, vegetables, and steak between 4 serving bowls or plates. Serve immediately, with Yum yum sauce and green onions as a garnish.