Combine the sauce ingredients: add the coconut aminos, chicken broth, rice vinegar, toasted sesame oil, tapioca flour, peeled ginger, sea salt, and sriracha (if using) to a small blender and blend until smooth; alternatively whisk thoroughly in a small bowl. Set aside.
Heat 2 tablespoons avocado oil in a large 12-inch nonstick skillet or wok over high heat until shimmering.
Add the sliced onion and sauté, stirring often, until edges begin to brown, about 2–3 minutes.
Add the chopped chicken and minced garlic; stir to combine and cook, stirring occasionally, until the chicken is browned but not fully cooked through, about 4–5 minutes. Reduce heat to medium if it cooks too quickly.
Stir in the broccoli florets and diced red bell pepper, then pour the prepared sauce over the mixture.
Cook, stirring occasionally, until the sauce thickens and the broccoli reaches your desired tenderness, about 4–6 minutes; taste and adjust salt and pepper as needed.
Serve the stir-fry over rice or cauliflower rice and garnish with sesame seeds and chopped cilantro, if desired.