Prepare the produce and chicken: cut chicken into 1-inch bite-size pieces; cut broccoli into florets; seed and cut bell peppers into 1-inch pieces; slice celery on a bias; chop scallions and separate whites from greens.
In a large mixing bowl, add the chicken and sprinkle with the cornstarch, 1 teaspoon salt, and 1/2 teaspoon cracked black pepper; toss until each piece is evenly coated.
Make the sauce in a small bowl or measuring pitcher by whisking together the oyster sauce, low-sodium soy sauce, chili garlic sauce, honey (or sugar), rice vinegar, and minced garlic; set aside.
Heat a wok or large deep skillet over medium-high heat and add the oil, swirling to coat. When the oil is hot, add the coated chicken and stir-fry for about 5 minutes until lightly browned on all sides and nearly cooked through; transfer chicken to a plate.
Add the scallion whites, sliced celery, and red and green bell peppers to the same pan; stir-fry for 2–3 minutes until they begin to soften.
Return the chicken and broccoli florets to the pan, pour the prepared sauce over everything, and stir to combine.
Simmer and stir for 3–4 minutes until the sauce thickens slightly and the broccoli is tender-crisp. Sprinkle the scallion greens over the top and remove from heat.
Serve warm alongside jasmine rice, brown rice, or cauliflower rice if desired.
