Season chicken breasts with half of the salt and pepper.

Grill chicken over medium-high heat for 6 to 7 minutes per side until the internal temperature reaches 165°F (74°C).

Remove chicken from heat and let rest for 5 minutes before cutting into 3/4-inch cubes.

In a small whisking bowl, emulsify the olive oil, lime juice, remaining salt, and remaining pepper.

In a large chilled mixing bowl, combine the cubed watermelon, red onion, and grilled chicken.

Drizzle the lime dressing over the salad and toss gently to incorporate.

Garnish with crumbled feta and torn mint leaves immediately before serving to maintain texture.