Using a 2- 3 inch cookie cutter, cut the watermelon into 8 rounds. Slice the radishes thin and set aside.
Pat the scallops dry and remove the “foot.” Sprinkle with salt, pepper and cayenne pepper.
Heat a large skillet to high. Drizzle a scant amount of oil in the skillet and carefully rub it around with a paper towel. When the skillet is smoking; place the scallops top down. Sear for 1 1/2 minutes until you can see carmelization around the edges.
Using tongs or a metal spatula, flip the scallops. Add 1 tablespoon of butter to the skillet and cook 1-2 more minutes.
Puree the mint, vinegar, grape seed oil, agave, salt and pepper in the blender. To assemble: Place a handful of arugula on a plate. Add one watermelon round on the arugula, followed by a scallop. Arrange the radishes around and drizzle with mint vinaigrette.
Makes 8 first-course servings, or 2-4 dinner servings.