Prepare the ingredients: slice chicken, vegetables, and mince garlic and ginger.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add the sliced chicken breast to the pan, cooking until browned and cooked through, about 5-7 minutes.
Stir in the garlic and ginger, cooking for an additional minute until fragrant.
Toss in the mushrooms, bell pepper, broccoli, and snow peas; stir-fry for 3-4 minutes.
Add the soy sauce and oyster sauce, stirring to coat the mixture evenly.
Pour in the cornstarch slurry, continuing to stir until the sauce thickens, about 1-2 minutes.
Taste and adjust seasoning if necessary, then remove from heat.
Serve immediately over rice or enjoy on its own, garnished with sesame seeds or scallions if desired.