This deceptively simple and well-balanced salad combines a variety of flavors and textures -- tart, creamy, peppery -- and comes together in a snap.
Make dressing: In a large bowl, whisk together vinegar, sugar, and oil until combined.
Peel and cut grapefruit into segments (reserve juice for another use). Add watercress, avocado, and grapefruit to bowl with dressing. Season with salt and pepper; toss gently to combine. Serve.
Ruby red grapefruit are available year-round but peak from October through March. Choose those that feel heavy for their size, and look for a smooth, thin, blemish-free yellow skin (sometimes with some pink or green).