Heat oil in a large heavy skillet over high heat. Add chicken pieces, and fry, stirring, until browned. Pour in the vinegar, soy sauce, and sugar; stirring to dissolve sugar. Season with red pepper flakes, garlic powder, onion powder, and ginger. Reduce heat to low, cover, and simmer for 15 minutes. Taste the sauce at this point and adjust seasoning to taste. The sauce should be very sweet. If it is too tart, add more sugar; if it is too sweet, add more vinegar.Advertisement
Once the sauce is to your liking, add the mushrooms, peas, and green onions. Simmer gently over low heat for another 5 minutes, until the mushrooms shrink a bit. Stir together the cornstarch and water, and stir it into the sauce. Continue to simmer until it reaches the desired thickness.