Cook bacon in a large skillet over medium, stirring occasionally, until golden brown and crisp around edges, 10–12 minutes. Using a slotted spoon, transfer to paper towels to drain. Pour off all but 1 Tbsp. bacon fat from skillet. Season pears with salt and pepper and cook in skillet with bacon fat over medium high, turning occasionally, until golden brown and starting to soften (they should be slightly firm at cores), 5–7 minutes. Transfer to a platter; let cool. Meanwhile, whisk vinegar, mustard, and oil in a small bowl to combine; season dressing with salt and pepper. Toss walnuts with remaining 2 tsp. oil in another small bowl; season with salt. Drizzle dressing over pears and scatter walnuts and bacon on top. Just before serving, top with chives. Dish (without chives) can be made 3 hours ahead. Store tightly wrapped at room temperature.
*I made this recipe first as Bon Appétit recommends, and a second time without the bacon. They were both delicious but, no surprise, better with bacon. You can substitute the residual bacon fat with olive oil to cook your pears.