Prepare the sauce: In a medium bowl, whisk the cornstarch with water until smooth and free from clumps. Add light soy sauce, mirin, light brown sugar, freshly grated ginger, and garlic cloves. Whisk again and set aside.
Heat the pan: Preheat a large skillet or wok over medium-low heat, then add olive oil.
Cook the vegetables: Add the chopped broccoli, thinly sliced carrots, red bell pepper strips, snow peas, and asparagus pieces. Cover with a lid and let them steam and soften for a few minutes.
Add the sauce: Pour the prepared teriyaki sauce over the vegetables. Stir well and cook for about 5 minutes, until the sauce thickens into a glossy coating and the veggies are tender-crisp.
Finish and serve: Sprinkle with sesame seeds and fresh green onion. Serve and enjoy!