Prep everything first. Slice the chicken thinly against the grain. Chop all vegetables and set them in separate piles.
Stir fries move fast, so having everything ready makes a big difference.
Make the sauce. In a small bowl, whisk soy sauce, chicken broth, vinegar, sesame oil, sweetener, and chili garlic sauce if using. Sprinkle in xanthan gum and whisk well. It thickens as it heats, so don’t overdo it.
Set aside.
Heat the pan properly. Use a large skillet or wok and place it over medium-high to high heat. Add 1 tablespoon oil and let it shimmer. Hot pan = good sear and less sticking.
Cook the chicken in batches. Add half the chicken in a single layer.
Season lightly with salt and pepper. Cook 2–3 minutes per side until golden and just cooked through. Transfer to a plate.
Repeat with remaining chicken, adding a little oil if needed.
Stir fry the vegetables. Add another teaspoon of oil if the pan is dry. Toss in broccoli and onion first and stir fry for 2 minutes. Then add bell pepper, zucchini, and snow peas.
Cook 2–3 minutes more, stirring often. You want crisp-tender, not soft.
Add aromatics. Push veggies to the sides, add garlic and ginger to the center, and cook 30 seconds until fragrant. Mix everything together.
Combine with sauce. Return the chicken and any juices to the pan.
Pour in the sauce and toss to coat. Let it bubble for 1–2 minutes until glossy and slightly thickened.
Taste and finish. Adjust salt, sweetness, or heat. Top with green onions and sesame seeds.
Serve immediately.