In a bowl, season chicken with salt and pepper. Add cornstarch and stir to coat meat thoroughly. Marinate for about 20 minutes.
In a bowl, combine water, soy sauce, oyster sauce, Chinese cooking wine, sugar, and pepper to taste. Stir until well-blended and sugar is dissolved. Set aside.
In a wide, heavy-bottomed pan or wok over medium-high heat, heat one tablespoon of oil. Add snow peas and cook for about 20 to 30 seconds or until tender-crisp. Remove from pan and drain on paper towels.
Add another tablespoon of oil as needed. Add chicken and cook, occasionally stirring, for until lightly browned and fully cooked.
Add onions and garlic and continue to cook for about 1 to 2 minutes.
Add sauce mixture to pan, stirring to combine. Bring to a simmer until it begins to thicken.
Add cashews and snow peas. Continue to cook for about 1 to 2 minutes or until heated through.
Remove from pan and transfer to serving platter. Garnish with additional cashews, if desired. Serve hot.