1 (12-oz.) head radicchio, halved, cored, and sliced thin lengthwise (about 5 cups)
1 small fennel bulb, halved, cored, and sliced thin lengthwise
1 Tbsp. chopped fennel fronds
1 celery rib, sliced thin
3 Tbsp. extra-virgin olive oil
2 Tbsp. lemon juice
1/2 tsp. salt
1/4 tsp. pepper
1 ripe Bartlett pear, halved, cored, and sliced into thin matchsticks
1 cup walnuts, chopped coarse
3/4 cup grated Parmesan cheese