Waldorf salad - Good Food Middle East

Ingredients

• 50g walnuts , toasted and roughly chopped
• 2 apples (we used Granny Smith), roughly chopped
• 1 lemon , juiced
• 100g mayonnaise
• 2 tbsp Greek-style yogurt
• ½ tbsp Dijon mustard
• 150g red grapes , halved
• 3 celery sticks, finely sliced
• 1 romaine or Little Gem lettuce , leaves separated and torn if large