Cut off the florets of 1 bunch broccoli; peel and thinly slice the stems. Heat 2 tablespoons vegetable oil in a large skillet over medium-high heat; add 4 smashed garlic cloves and 4 thin slices ginger and stir-fry until just golden, 1 minute. Add the broccoli, 1/4 teaspoon kosher salt and 1/2 cup water. Stir-fry until crisp-tender, 4 minutes. Stir in 2 tablespoons oyster sauce, a splash of white vinegar and some cashews.