In a large skillet over medium to medium-high heat, add the butter.
Add the onion and carrot and allow to cook until the onions are soft, about 6 minutes. Add in the peas, corn, and Brussels sprouts and cook until the Brussels sprouts are wilted, about 3 minutes.
Add the chicken.
While the veggies are cooking, make the sauce. Mix together the soy sauce, water, garlic, brown sugar, and cornstarch in a bowl until well combined.
Pour the sauce over the chicken and veggie mixture and allow to cook until thickened, about 5 minutes.
Serve over rice or noodles.