Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners.
In a bowl, whisk together flour, baking powder, and salt. Set aside.
In a separate bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Stir in vanilla extract.
Gradually mix in dry ingredients, alternating with milk. Fold in diced mango, strawberries, lime zest, lime juice, and tequila if using.
Divide batter evenly into cupcake liners, filling about ¾ full. Bake for 18 minutes or until a toothpick inserted in the center comes out clean. Cool completely before frosting.
Beat butter until creamy. Gradually add powdered sugar, mixing until smooth. Add lime juice, tequila (if using), and fruit purees. Mix until well combined.
Pipe frosting onto cooled cupcakes and garnish with lime zest and coarse sugar.