In a small bowl, whisk together soy sauce, mirin, sake, brown sugar, ginger, and garlic. Set aside.
Heat vegetable oil in a large skillet over medium-high heat. Add mushrooms and cook, stirring occasionally, until golden brown and tender, about 5-7 minutes.
Pour the teriyaki sauce over the mushrooms. Stir in the cornstarch slurry and cook, stirring, until the sauce thickens and coats the mushrooms, about 1-2 minutes.
Divide rice between two bowls. Top with teriyaki mushrooms, steamed broccoli, and shredded carrots.
Garnish with sesame seeds and green onions. Serve immediately.
Tips
For a spicier kick, add a pinch of red pepper flakes to the sauce.
Substitute any vegetables you have on hand, such as snap peas or bell peppers.
To make it vegan, ensure your sugar is vegan-friendly and skip the sake or use a vegan substitute.