Curry Chicken Sandwich

2 cups cubed cooked chicken breast
3/4 cup chopped apple
3/4 cup dried cranberries
3/4 cup mayonnaise
1/2 cup chopped walnuts
1/2 cup chopped celery
2 teaspoons lemon juice
1 tablespoon chopped green onion
1 teaspoon curry powder
6 lettuce leaves
6 croissants, split