In a small bowl, whisk together the soy sauce, rice vinegar, water, cornstarch, and crushed red pepper flakes. Set aside.
Heat the olive oil in a large non-stick skillet or wok over medium-high heat.
Add the minced garlic and grated ginger to the skillet and sauté for 30 seconds until fragrant.
Add the chicken pieces to the skillet and season with salt and black pepper. Cook for 5-7 minutes, stirring occasionally, until the chicken is cooked through and lightly browned.
Add the broccoli florets to the skillet and stir-fry for 3-4 minutes until they are bright green and tender-crisp.
Pour the soy sauce mixture over the chicken and broccoli. Stir well to coat everything evenly.
Cook for an additional 2-3 minutes, stirring frequently, until the sauce has thickened and everything is heated through.
Remove from heat and serve immediately.