Heat 1 tablespoon of the oil in a large nonstick skillet over medium-high heat. Sprinkle pork with 1/4 teaspoon each of the salt and pepper. Add pork to skillet and cook for about 3 to 5 minutes per side, or until internal temperature reaches 140° on an instant read thermometer. Reduce heat to low if pork becomes too browned. Remove pork to a serving platter and keep warm.
In the same skillet, heat remaining 1 tablespoon oil over medium-high heat. Add onion, garlic and chard stalks and cook until beginning to soften, about 4 minutes. Add leaves, remaining 1/4 teaspoon each of the salt and pepper, broth and raisins. Stir to combine then cover, reduce heat to medium-low, and cook for about 6 minutes or until tender and wilted, stirring occasionally.
Remove lid and increase heat to medium-high and cook, stirring, for about 3 minutes or until most of the liquid has evaporated.
Remove chard mixture from heat. Let cool for 5 minutes, then stir in yogurt, vinegar and pine nuts. Serve with pork immediately.