Cube watermelon, cantaloupe, and honeydew into 1" cubes. Place into large bowl or serving platter.
Top with a drizzle (2-3 TBSP) olive oil and juice of 3 limes.
Lightly toss.
Add thinly sliced red onion, feta cheese crumbles, and roughly chopped mint leaves.
Top with fresh cracked black pepper.
Serve chilled.