In a small bowl, whisk together 1 tablespoon water, the oyster and soy sauces, cornstarch and ¼ teaspoon each salt and pepper.
In a 12- to 14-inch wok or a 12-inch nonstick skillet over medium, heat 2 tablespoons oil until shimmering.
Add the chicken and cook, stirring occasionally, until opaque throughout, 3 to 4 minutes; transfer to a plate.
To the now-empty pan over medium-high, add the remaining 1 tablespoon oil and the ginger. Cook, stirring, until fragrant, about 30 seconds.
Add the peas and cook, stirring, until they deepen in color, about 2 minutes.
Stir in the chicken and accumulated juices.
Whisk the sauce mixture to recombine, then stir into the pea-chicken mixture.
Cook, stirring, until the sauce is simmering and glossy, about 2 minutes.
