Heat the oven to 400 degrees. Place the finely chopped peanuts in a shallow dish. Season with salt and pepper. Roll the goat cheese log in the peanuts to evenly coat. Refrigerate until firm if necessary, then cut evenly into 4 rounds.

Arrange pears, cut side down, in a baking pan. Pour butter over the pears and toss to coat. Return pears to cut side down position. Roast until tender, about 25 minutes. Arrange pears cut side up in the baking dish. Place rounds of peanut-crusted goat cheese on top in the scooped center. Continue to roast 5 minutes more, until the cheese is melted and soft.

Meanwhile, whisk together the shallot, mustard, and vinegar. Add oil in a slow stream, whisking until emulsified, and season with salt and pepper. Just before serving, toss salad greens with just enough dressing to coat. Remove pears from the oven and serve each salad topped with a roasted pear topped with goat cheese.