Preparation Heat oil in heavy large skillet over medium heat. Add leeks and bell pepper. Sauté until just beginning to soften, about 5 minutes. Add cauliflower, tomatoes and tarragon and cook until cauliflower is tender, stirring occasionally, about 20 minutes. Season with salt and pepper. Pour sauce over pasta. Serve, passing Parmesan separately.
Preparation Heat oil in heavy large skillet over medium heat. Add leeks and bell pepper. Sauté until just beginning to soften, about 5 minutes. Add cauliflower, tomatoes and tarragon and cook until cauliflower is tender, stirring occasionally, about 20 minutes. Season with salt and pepper. Pour sauce over pasta. Serve, passing Parmesan separately.