Combine sherry, sesame seed oil, ginger root, garlic, soy sauce, and pepper in a glass bowl. Add chicken and stir to coat thoroughly. Cover and marinate chicken for at least 2 hours before stir-frying. For best results, marinate 6 to 8 hours. Pour off marinade liquid before stir-frying.
Combine cornstarch with chicken stock. Whisk thoroughly in a bowl or shake together in a small glass jar until cornstarch is dissolved.
Preheat your Calphalon stir-fry pan on medium to medium-high heat. When the rim of the pan is hot-to-the-touch, add oil and heat for another minute. Add scallions and stir-fry for ½ minute. Add red bell peppers and stir-fry for 1 minute. Add mushrooms and stir-fry for 1 minute more. Remove vegetables from pan and set aside in a large bowl. Add 1-½ teaspoons of oil to pan, heat, add snow peas and stir-fry for 2 minutes. Set aside with other vegetables. Add 1 tablespoon of oil to pan, heat, add chicken and stir-fry 5 minutes or until chicken is cooked through. Put vegetables back in stir-fry; add the chicken stock and cornstarch mixture. Bring sauce to a boil, stir all ingredients together and heat through. Season to taste with soy sauce and black pepper.
Serve immediately over rice. Garnish with sliced almonds if desired.