Prep the chicken: Pat dry and slice into thin strips. Toss with a pinch of salt, pepper, and 1 teaspoon soy sauce.
Optional: add 1 teaspoon baking soda, toss, and rest 10 minutes for extra tenderness; rinse and pat dry before cooking.
Make the sauce: In a small bowl, mix 3 tablespoons tamari/soy, 1 tablespoon rice vinegar, 1/2 teaspoon sesame oil, 1/2 teaspoon fish sauce (optional), 1–2 teaspoons sweetener, and chili flakes or sriracha to taste. If using a thickener, sprinkle in xanthan gum and whisk well.
Heat the pan: Set a large skillet or wok over medium-high heat. Add 1 tablespoon oil and swirl until shimmering.
Sear the chicken: Cook in two batches so it browns, 2–3 minutes per side, just until cooked through.
Remove to a plate.
Stir-fry the veggies: Add another teaspoon of oil if needed. Stir-fry broccoli and snap peas first for 2 minutes. Add peppers, zucchini, mushrooms, and onion; cook 3–4 minutes until crisp-tender.
Add aromatics: Push veggies to the sides.
Add a small drizzle of oil, then the garlic and ginger. Stir 30 seconds until fragrant.
Combine and sauce: Return chicken and juices to the pan. Pour in the sauce and toss for 60–90 seconds until glossy and everything is coated.
Adjust salt, heat, or sweetness to taste.
Finish and serve: Turn off heat. Sprinkle sesame seeds and scallions. Squeeze lime over the top.
Serve as-is, or spoon over warm cauliflower rice.