4 lb. watermelon
2 Valencia oranges
2/3 cup packed light brown sugar
1/2 cup apple cider vinegar
1 medium shallot, thinly sliced
1/2 medium jalapeño, finely chopped (with ribs and seeds)
1 T bs. very finely ground coffee beans (preferably French roast)
2 tsp. packed light brown sugar
1 tsp. chili powder
2 T bs. extra-virgin olive oil
2 1-lb. pork tenderloins, trimmed
For the relish:
Cut the flesh away from the watermelon rind. Cut enough of the flesh into 1/4-inch dice to yield 1/2 cup (reserve the rest for another use). Using a vegetable peeler, remove the dark-green skin from the rind and discard. Cut the rind into 1/4-inch dice; you should have about 3 cups.
Slice the ends off one of the oranges. Stand the orange on one cut end and cut off the peel and white pith to expose the flesh. Cut the orange segments from the membrane, cut each segment into 3 pieces, and put them in a small bowl. Squeeze the juice from the membrane into the bowl. Repeat with the remaining orange.
In a 3-quart saucepan, combine 2/3 cup water with the watermelon flesh and rind, orange segments and juice, brown sugar, vinegar, shallot, jalapeño, and 1/4 tsp. salt. Bring to a boil over medium-high heat, stirring occasionally, until the sugar dissolves, about 4 minutes. Reduce the heat to low and simmer, stirring occasionally, until the rind is translucent and the mixture thickens, about 40 minutes. Season to taste with salt, and let cool to room temperature.
For the pork:
In a small bowl, combine the coffee, brown sugar, chili powder, and 2 tsp. salt. Add the olive oil and mix well. Rub the mixture evenly over the pork and set aside.
Prepare a medium-high gas or charcoal grill for indirect cooking.
Put the tenderloins on the hot side of the grill, cover, and cook, flipping once, until grill marks form on 2 sides, about 4 minutes per side. Move the tenderloins to the cooler side of the grill and continue to cook, covered, until the internal temperature of the pork reaches 140°F to 145°F, 7 to 9 minutes. Transfer to a cutting board, tent with foil, and let rest for about 10 minutes.
Slice the pork and serve with the watermelon rind relish.