Heat 2 tablespoons of the olive oil in a wok or large nonstick frying pan over medium-high heat until shimmering. Add the celery and cook, stirring often, until bright green and beginning to soften, about 2 minutes. Add the garlic and ginger and cook until fragrant, about 1 minute. Add 8 ounces ground pork and 1/2 teaspoon Chinese five-spice powder if using and cook, breaking up the pork with the back of a spoon, until cooked through, lightly browned, and any liquid has evaporated, 3 to 4 minutes. Add the cabbage and 1 cup bean sprouts and cook, stirring often, until the cabbage is wilted, about 4 minutes.