Watermelon is the star in this refreshing summer ceviche. Make this dish while the fruit is at its peak and bursting with flavor - the sweetness mellows out the intense acidity from the lime juice. If you’re sensitive to heat, add the serrano pepper sparingly.
In a medium non-reactive bowl, combine the cubed fish with the lime juice and season with salt. Cover with plastic wrap and refrigerate until the fish is firm and opaque, 2 to 3 hours.
In a separate medium bowl, toss the watermelon with the cucumber, serrano and red onion. Season lightly with salt and let sit for at least 20 minutes.
Drain the fish and discard the lime juice. Gently fold the fish and the orange juice into the watermelon mixture. Season with salt and pepper. Transfer to a serving bowl and garnish with avocado, radish and cilantro. Serve right away with tortilla or plantain chips for scooping.