Marinate the chicken: Add the sliced chicken to a bowl with the soy sauce, cornstarch, egg white, water, salt, and pepper. Mix, cover, and marinate in the refrigerator for 15-30 mins.
Make the sauce: In a medium glass measuring cup (or bowl), mix the chicken broth, cornstarch, soy sauce, oyster sauce, sesame oil, vinegar, sugar, and pepper.
Bring a pot (or wok) of generously salted water to a boil. Place the broccoli florets in the boiling water and cook for 1 min, then drain and set aside.
In a large wok (or pan) preheated over medium high heat, add 1 Tbsp avocado oil and the chicken. Stir fry the chicken until cooked through (3-5 mins) then remove from the pan.
Add 1 more Tbsp avocado oil along with the garlic and ginger. Stir fry for 1 min until fragrant and then add the broccoli and stir fry for 2-4 more mins until the broccoli is almost to your desired tenderness (I like mine a little al dente).
Add the sauce and stir fry for 1-2 more mins until sauce thickens, then add the chicken and scallions and stir fry 1-2 more mins until the chicken gets heated back through. Taste and adjust seasoning if desired. Serve over rice and enjoy!