Cut cucumbers into quarters lengthwise. Cut off the seeds. Then cut each strip diagonally into ¼ inch thick pieces.
Place cucumber pieces in a bowl. Add rice vinegar, salt, and granulated sugar. Mix well and allow it to pickle for 30 minutes. Discard the pickling solution.
Heat a large wok or fry pan. Add vegetable oil. When oil is hot, add red onion and chili strips. Stir fry for 2 minutes. Then add garlic and fry for another 30 seconds.
Add shrimps, pickled cucumbers, and soy sauce. Stir fry until shrimps curl and turn pink, about 3 minutes.
Add cornstarch mixture. When sauce thickens, turn off stove. Transfer to a dish.
Serve immediately with steamed rice.