Combine the fish sauce, lime juice and sugar in a small bowl. Stir to dissolved the sugar.
Heat the oil in a wok or skillet over high heat.
Brown the chicken in batches, if necessary to make sure the chicken gets nice and brown. About 3-5 minutes.
If cooking the onions add them now and cook for about a minute or 2 to soften.
Add the garlic and peppers and cook until fragrant about a minute.
Turn off the heat and stir in the fish sauce mixture.
In a large bowl, combine the chicken, mint leaves and cucumbers and toss to combine.
Video
Notes
Can substitute ground turkey or ground beef. If using beef, you can omit the oil. Serve this as a light salad or with rice or noodles. Can toss the onions raw at the end with the cucumbers and mint, instead of cooking them, if you prefer.