Preheat oven to 400 degrees F (200 degrees C). Spread pecans evenly on a baking sheet. Toast for 8 to 10 minutes, or until lightly browned and fragrant.
In a small bowl, stir together the vinegar, mustard, sugar, salt, and pepper; mix until sugar and salt dissolve. Whisk in olive oil.
In a salad bowl, toss together the greens, cranberries, pecans, onions, and cheese. Drizzle with vinaigrette, and toss gently to coat.