Toast the pecans in a medium sauté pan, over medium heat. Stir constantly and remove as soon as the pecans begin browning.
Whisk together the vinegar, shallot, and mustard in a large bowl and then whisk in the olive oil and add salt and pepper, to taste.
Add the lettuce, duck, and cheese to the large bowl and toss to coat with the dressing. Sprinkle salad with berries and pecans before serving.