“Stuffed” Butterflied Pork Tenderloin

1 (3-pound) pork tenderloin

1 small yellow onion, thinly sliced

1 pint cherry tomatoes

5 ounces baby arugula or spinach

1 cup crumbled feta

Salt, pepper, oil

Heat oven to 425F. 

Cut tenderloin in half lengthwise, leaving about 1/2 an inch still connected, then flatten both halves with your hands. 

Heat oil in an ovenproof skillet large enough to hold the tenderloin flat. Season with salt and pepper, then brown both sides of the pork. Remove to a plate and add onions to the pan. Cook, stirring, until golden, about 6 minutes, then add tomatoes. Cook until soft, about 5 minutes. Then add arugula and cook until wilted, about 3 minutes. 

Season filling lightly with salt and pepper, then spoon on top of tenderloin. Transfer back to the pan and top with feta. 

Roast in oven until the internal temperature of the pork is 140F, about 14 minutes. Remove from oven and let stand 5 minutes, then slice and serve.