Toss together the sliced chicken and cornstarch in a large bowl. Whisk together the oyster sauce, fish sauce, soy sauce and sugar in a small bowl.
Heat the oil in a wok or large nonstick skillet over high heat until the oil begins to smoke. Add the chicken and cook until just cooked through, about 4 minutes. Remove to a plate.
Add the onion and red bell pepper and cook for about 2 minutes. Add the ginger, garlic and Thai chile pepper and cook for another minute. Stir in the riced cauliflower and cook 1 minute. Stir in the oyster sauce mixture and continue to cook until the cauliflower is cooked throughout, another 1 to 2 minutes.
Transfer to a serving bowl and finish with a squeeze of lime juice. Garnish with the scallions, toasted peanuts and cilantro leaves.