Combine all ingredients and whisk until cornstarch is completely mixed into sauce.
Two or three minutes before your stir fried ingredients are done, gradually add desired amount of mixed sauce, and continuously stir until sauce is heated through and looks shiny.
Cut ends from cucumbers, slice in half vertically and scoop out seeds. Cut into 2 inch sections lengthwise and then into 1/4 inch sticks. Set aside.
Prepare sauce and set aside.
Heat wok or pan over medium high heat. Add oil. When hot, add garlic and ginger and stir-fry 20 seconds. Add shrimp and stir-fry for 3 minutes. Remove from pan and add cucumbers and onions. Stir-fry for 1 minute. Add shrimp and sauce to pan. Bring to a boil, increasing heat if necessary. Stir until sauce thickens and you're done!