Apple Salad

2 tbs olive oil
2 tsp fresh lemon juice
1/2 tsp coarse-grain Dijon mustard
1 (1-pound) head red leaf lettuce, torn into bite-size pieces (8 cups)
1 avocado, pitted, peeled and thinly sliced
1/2 granny smith apple, thinly sliced
salt and freshly ground black pepper

Combine oil, lemon juice, and mustard in a jar. Add a pinch of salt and pepper, close tightly and shake vigorously to combine. Toss dressing with lettuce; add salt and pepper to taste. Distribute salad among plates, top with avocado and apple slices, and serve.