Make dressing: Whisk olive oil, vinegar, mustard, honey, salt, and pepper until emulsified.
Assemble salad:
3 Toss greens, fennel, and pear slices in a large bowl with dressing.
4 Scatter toasted hazelnuts and crumbled cheese on top.
5 Add sliced chicken if making it a main dish.
6 Serve immediately while pears are crisp.