In a small bowl, whisk together the olive oil, Dijon mustard, honey (reserve one tablespoon), lemon juice, and black pepper.

In a large mixing bowl, combine the baby spinach, diced mango, blueberries, walnuts, and crumbled Feta cheese.

Drizzle the dressing over the salad mixture and gently toss until everything is well coated.

Transfer the salad to a serving platter or individual bowls and serve immediately.