Stir the shrimp, mango, and green onion together in a bowl; set aside.
Whisk the lime juice, honey, and cayenne pepper together in a separate bowl until blended, making sure to scrape along bottom of bowl as needed to incorporate honey; pour over the shrimp mixture. Cover with plastic wrap and refrigerate 30 minutes.
Preheat an oven to 350 degrees F (175 degrees C).
Arrange the bread slices on a baking sheet. Top each bread slice with a slice of Brie cheese.
Bake in the preheated oven until slightly browned and the Brie cheese is soft and melted, about 5 minutes. Top each slice with 1 tablespoon of the shrimp mixture to serve.
