In a small bowl, combine soy sauce, oyster sauce, rice vinegar, sesame oil, crushed red pepper flakes, and 1/4 cup water. Set the sauce mixture aside.
In another small bowl, mix cornstarch and 1 tablespoon cold water until smooth. Set aside.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add minced garlic and ginger to the skillet and sauté for 30 seconds until fragrant.
Add ground turkey to the skillet. Season with salt and black pepper. Cook, breaking it up with a spatula, until browned and cooked through, about 6-8 minutes.
Add broccoli florets to the skillet and stir to combine with the turkey.
Pour the sauce mixture over the turkey and broccoli. Stir well to coat.
Cover the skillet and cook for 5 minutes, allowing the broccoli to become tender but still crisp.
Remove the lid and stir in the cornstarch slurry. Cook for another 1-2 minutes until the sauce thickens.
Taste and adjust seasoning with additional salt or pepper if needed.
Remove from heat and garnish with sliced green onions.
Serve immediately with steamed rice or noodles if desired.