Slice pork into 1-1/2" cubes. Season with pepper and 1 1/4 tsp salt then set aside.

Soffritto: Put walnuts in a food processor and pulse until chopped. Transfer to a small, heavy-bottomed saucepan and cover with the oil. Put garlic in the food processor and pulse until minced. Gradually bring the oil and walnuts to a low simmer, stirring frequently until the walnuts start to brown, about 2 minutes. Stir in minced garlic, then turn off the heat and continue to stir as the garlic cooks in the oil, about 1 minute. Let cook to room temperature. Stir in cherries.

Spiedini: Turn on grill. While grill is heating up, prepare six skewers. Toss pork in olive oil to coat. Thread pork and two prunes per skewer. Sear pork over the hottest parts of the grill, then move to the side to continue to render the meat until cooked, but still juicy, about 8-10 minutes total.

Arrange a bed of argula on a platter. Place skewers on top. Stir lemon juice and remaining 1/2 tsp salt into soffritto then spoon over the pork and arugula. Serve with lemon wedge.