In a small bowl, whisk together the soy sauce, vegetable stock, and cornstarch, set aside.
Heat the oil in a large skillet or wok over medium-high heat.
Add the shiitake mushrooms, bell peppers, ginger, and garlic. Cook, stirring constantly, 5 minutes.
Add the carrots, snap peas, and scallions and cook 2 more minutes, stirring constantly.
Stir in the soy sauce mixture. Cook for 2 more minutes, until the sauce comes to a boil and thickens.
Serve over brown rice and top with toasted sesame seeds.