In a large bowl, add the cucumber, rice vinegar, water, red onion, sugar, and sesame oil. Mix well. Set it aside.
For the Thai Pork Stir Fry
In a large pan, heat the oil over medium-high heat. Add the pork to the skillet. Cook, breaking it up with the side of a spoon, until it is no longer pink, about five to six minutes. Add the garlic, ginger, and chili. Cook, stirring, until it becomes fragrant, about 30 seconds. Stir in the soy sauce, brown sugar, and fish sauce. Add the lime juice and continue to cook until the pork begins to brown, about one to two minutes.
Serve the stir-fry immediately with the cucumber salad and cilantro or store in the refrigerator for up to three days.