Heat vegetable oil in a large skillet or wok over medium-high heat.
Add minced garlic and sauté until fragrant.
Add sliced chicken breast and cook until lightly browned.
Stir in bell peppers and carrots; cook for 3-4 minutes.
Add broccoli florets and cook for another 2 minutes.
Mix in bean sprouts and stir well.
Pour in soy sauce and oyster sauce; stir to combine.
If desired, mix cornstarch with a little water and add to the pan for thickening.
Season with salt and pepper to taste.
Cook for an additional 2 minutes until everything is heated through.