Prepare the Watermelon. Cut the watermelon into 1-inch thick slices. Trim off the rind, creating steak-like rectangles or wedges.
Season. Brush both sides lightly with olive oil. Sprinkle with salt and black pepper.
Preheat the Grill. Heat your grill or grill pan over medium-high heat until hot.
Grill the Watermelon. Place the watermelon steaks directly on the grill grates. Cook for 3-5 minutes per side, until grill marks appear and the edges begin to caramelize.
Serve. Transfer to a platter and garnish with fresh mint, lime juice, or a drizzle of balsamic glaze if desired.