Heat cooking oil in a large skillet or wok over medium-high heat.

Add sliced chicken breast to the skillet and sauté for about 5 minutes, or until cooked through.

Add frozen vegetables, garlic powder, salt, and pepper to the skillet with the chicken.

Sauté the mixture until the vegetables are tender-crisp, about 5-7 minutes.

While the chicken and vegetables are cooking, prepare brown rice according to package directions in a separate pot or microwave.

Once the vegetables are tender-crisp, drain off any excess broth from the skillet.

Pour teriyaki sauce over the chicken and vegetables.

Heat the mixture through, stirring occasionally, until the sauce is heated through and evenly distributed, about 2-3 minutes.

Serve the chicken and vegetable stir-fry over prepared brown rice.