In a large bowl combine the cantaloupe, watermelon, cucumber, jicama, red onion and serrano peppers (if using). Toss to combine. Add the queso fresco.
In a small bowl combine the lime zest and agave. Cut the lime in half and add 3 tablespoons fresh lime juice to the agave mixture. Stir to combine and pour over the salad. Toss until the fruit and veg are coated. Chill for 30 minutes.
Sprinkle mint and additional queso fresco on the salad.