CUBE the watermelon into bite-sized pieces. Set aside.
SLICE the onion thinly, to prepare pickled onions, using mandoline for even cuts if you have one available.
COMBINE the remaining pickling ingredients in a small saucepan and bring to rapid boil, then remove from the heat. Place the sliced onions in heat-proof jar and pour the liquid over to evenly coat. The onions should soften within 15 minutes, depending on thickness.
COMBINE the red wine vinegar, lemon juice, and salt in a small bowl. Slowly whisk in the olive oil until incorporated.
DRESS the arugula lightly to taste and toss in a mixing bowl, then place it in a serving dish. Top it with the cubed watermelon, crumbled cheese, and pickled onions. Finish with any remaining vinaigrette, if desired.
For more recipes that will inspire you to eat thoughtfully and love joyfully, visit Food52.com!