Sauté pancetta and shallot in a large skillet over medium heat 5 minutes or until browned. Add mirin and wine vinegar; simmer 2 minutes. Whisk in oil. Set aside, and keep warm.
Combine sliced endive, celery, apple, and mushrooms; sprinkle with lemon juice, and toss well. Arrange salad on individual serving plates. Tuck several endive leaves around edge of each salad. Drizzle with reserved warm dressing, and sprinkle with blue cheese.