In a large bowl, toss the sliced chicken with the cornstarch until evenly coated. In a small bowl, whisk together the oyster sauce, fish sauce, soy sauce, and sugar. Set aside.
Heat the avocado oil in a wok or large nonstick skillet over high heat until it begins to smoke.
Add the chicken and cook, stirring occasionally, until just cooked through and browned, about 4 minutes. Transfer to a plate.
Add the onion and bell pepper to the pan and cook for 2 minutes, stirring frequently.
Add the ginger, garlic, and Thai chile; cook for 1 minute more until fragrant and browned. Stir in the riced cauliflower and cook for 2 to 3 minutes more.
Pour in the sauce mixture and stir to combine. Cook for another 1–2 minutes, until the cauliflower is heated through and evenly coated.
Transfer to a serving bowl and finish with a squeeze of lime juice. Garnish with scallions, chopped peanuts, and cilantro leaves before serving.
