Slice Onion: Cut the red onion into thin slices using a sharp knife for even pickling.
Quick Pickle Onions: Place the sliced onions in a bowl and pour the red wine vinegar over them. Toss well to coat all the slices.
Rest Onions: Let the onions sit at room temperature for about 15 minutes until slightly softened and lightly pickled.
Drain and Reserve Liquid: Strain the onions and set them aside, reserving about 2 teaspoons of the pickling liquid for later use.
Make Dressing: In a small bowl, mix the reserved pickling liquid with the olive oil until combined.
Prepare Watermelon Base: Slice a thick round of watermelon, keeping the rind intact to act as the “crust.”
Brush Watermelon: Lightly brush one side of the watermelon with the dressing mixture.
Grill First Side: Place the watermelon on a preheated grill over medium-high heat, brushed side down. Grill for about 3 to 4 minutes until grill marks form.
Flip and Grill: Brush the other side with the dressing, flip, and grill for another 3 to 4 minutes.
Add Toppings: Remove the watermelon from the grill and transfer to a cutting board. Evenly top with pickled onions, crumbled blue cheese, and chopped pecans. Sprinkle fresh herbs over the top for a bright, fresh flavor.
Slice and Serve: Cut into wedges like a pizza and serve immediately while slightly warm.