1. Whisk lemon zest and juice, shallot, mayonnaise, 1/4 teaspoon salt, 1/4 teaspoon pepper, and cayenne in nonreactive bowl until mixture appears milky and no lumps remain. Whisking constantly, slowly drizzle in oil. (Dressing should appear homogeneous, glossy, and slightly thickened, without any pools of oil on surface.)

2. Gently toss avocados, 2 tablespoons dressing, and 1/2 teaspoon salt in bowl. Transfer avocados to large platter or individual plates.

3. Toss mangos, jícama, basil, and mint with remaining dressing. Spoon mango mixture over avocados and sprinkle with feta. Serve immediately.

Serves 6