In a small bowl, whisk together the olive oil, lime juice, orange juice, garlic, sugar, salt, and pepper. Refrigerate until ready to use.
In a medium bowl, pour 2 to 3 tablespoons of dressing over the watercress and toss to coat. Transfer watercress to a serving platter, and top with the avocado, pineapple, radishes, and onion. Drizzle with more dressing to taste.
Notes
For extra depth of flavor sear the pineapple chunks in a skillet with 1 tablespoon of butter over medium-high heat.The dressing can be made up to 3 to 4 days in advance. Store in the refrigerator.Make this a complete meal by adding grilled chicken, shrimp, or steak to the salad.