Preheat oven to 425 degrees. Arrange asparagus and capers evenly on 2 rimmed baking sheets. Drizzle with oil, turning asparagus to coat. Season with salt, and sprinkle with red-pepper flakes. Roast, shaking sheets once, until asparagus is crisp-tender and golden at the tips, 12 to 16 minutes. Let cool slightly. Serve warm or at room temperature. Garnish with lemon wedges.