Prepare the vinaigrette: In a small bowl or jar, whisk together the olive oil, mandarin orange juice, honey, Dijon mustard, salt, and pepper until well emulsified.

Prepare the salad base: In a large mixing bowl, gently combine the mixed greens, sliced red onion, and the drained mandarin oranges.

Add the fruit and olives: Carefully fold in the diced mango and sliced black olives into the greens mixture. Be gentle not to crush the ingredients.

Toss lightly: Drizzle about two-thirds of the prepared vinaigrette over the salad components. Toss very gently to ensure everything is lightly coated. Add more dressing if necessary, reserving some for serving.

Final assembly: Just before serving, gently fold in the diced avocado. The avocado should be added last to prevent it from breaking down too much.

Serve immediately: Divide the salad onto chilled plates. Drizzle any remaining dressing lightly over the top of each serving.