Toast walnuts in a small dry skillet over medium heat (it will take about 3 minutes).
In a small saucepan, combine Champagne, cranberry sauce, shallots, Dijon mustard and oil. Whisk together. Set pan over high heat and bring to a boil. Simmer until reduced to about 1/3 cup (about 5 minutes). Remove from heat and season to taste with salt and black pepper.
Place greens in a large bowl. Top with pears, toasted walnuts and dried cranberries. Drizzle over cranberry vinaigrette just before serving.