In a small bowl, whisk together 3 tbsp oyster sauce, 1 tbsp soy sauce, 1 tsp cornstarch, pinch of sugar, and 1 tbsp water.
In a large skillet, heat 1 tbsp vegetable oil over medium high. Add 2 cloves garlic, diced. Add 1 head broccoli cut into florets.
Cook, tossing, until broccoli is bright green, about 3 minutes. Add 1/2 cup water, cover and cook until broccoli is tender. Add sauce mixture and cook until thickened.