• Whisk together mustard, vinegar, and salt and pepper to taste in a large bowl. Add 4 tablespoons oil in a slow stream, whisking until emulsified, then whisk in shallots.
• Heat remaining tablespoon of oil in a 10-inch heavy skillet over moderate heat until hot but not smoking, then cook pecans, stirring, until golden brown. Transfer nuts with a slotted spoon to paper towels to drain, then season with salt.
• Heat skillet with any oil remaining in it over moderately high heat until hot but not smoking, then brown duck on all sides until crisp, about 5 mins. Transfer to a cutting board and tear meat into bite-size pieces and discard bones. Keep duck warm, covered, on a baking sheet in oven.
• Halve and core pears and cut lengthwise into 1/4-inch-thick slices. Add pears, greens, duck, cheese, and nuts to dressing with salt and pepper to taste, then toss gently to combine.
