Fennel, Apple and Radicchio Salad with Walnuts

Ingredients

• 2 tbsp fresh lemon juice
• 1 tbsp brown sugar (packed)
• 1/2 tsp salt
• 1/4 tsp ground black pepper
• 1/4 cup Italian parsley (minced)
• 1/4 cup extra-virgin olive oil
• 1 tart green apple (unpeeled)
• 1 large fennel bulb ((about 300 g))
• 1 cup radicchio (thinly sliced)
• 1/2 cup walnuts (toasted and chopped, divided)
• Boston lettuce leaves