Using a sharp knife, butterfly the pork tenderloin. To do this, start at one end and make a lengthwise cut, stopping ½ inch from the other end. Open the tenderloin up like a book to make one large piece.
Heat the olive oil in a large skillet over medium-high heat. Add the onion and garlic and cook until softened, about 3 minutes. Add the mushrooms and chorizo and cook until the mushrooms are softened and the liquid has evaporated, about 5 minutes.
Stir in the smoked paprika, oregano, salt, and pepper. Remove the mixture from the heat and stir in the butter until melted. Let cool a few minutes.
Spread the pork tenderloin open and place the mushroom and chorizo filling down the center. Roll up the pork and tie with kitchen twine at 1-inch intervals. Place on a baking sheet and roast in preheated oven until the pork is cooked through, about 25 minutes.
Slice into 1-inch thick pieces and serve.
Interesting Facts
Pork tenderloin is an incredibly lean cut of meat that is low in fat and calories.
Chorizo is a type of spicy sausage that is made from pork or beef and flavored with garlic and chili peppers.
Smoked paprika is a type of spice made from ground smoked peppers.