Heat the oil in a wok or large skillet. When hot, add the onion, jalapeños, and garlic and stir-fry for 2 minutes, using a metal spatula to keep the ingredients in motion. Add the chicken and cook for 2 to 3 minutes, until the meat is beginning to brown on the outside. Add the fish sauce, sugar, soy sauce, and basil and cook for 1 minute more. Serve over rice.