1. In a large skillet, heat olive oil over medium-high. Add broccoli and cook until broccoli begins to brown, about 4 minutes. Add garlic, and cook, stirring occasionally, until broccoli is crisp-tender and garlic begins to brown, about 3 minutes. Add red-pepper flakes, season with salt and pepper, and transfer to a serving bowl. Toss with lemon zest and lemon juice, Parmesan, and walnuts. Serve warm or at room temperature.