In a small bowl, whisk together the olive oil, lime juice, minced garlic, and sea salt until well combined.
Arrange the cubed watermelon, cucumber, and sliced red onion on a large serving platter or bowl.
Drizzle half of the dressing evenly over the salad ingredients.
Top with crumbled feta cheese, avocado cubes, fresh mint leaves, and sliced jalapeño or serrano pepper if using.
Drizzle the remaining dressing over the top.
Season lightly with sea salt and serve immediately for the freshest flavor.
This Watermelon Salad with Feta & Mint tastes best chilled and freshly assembled.