Preheat the oven to 350°F. Butter an 8-inch square baking dish.
For topping, combine the butter, sugar, flour, oats and cinnamon in a bowl. Work together with fingertips until mixture resembles coarse meal. Toss in nuts; set aside.
Toss the apples with lemon juice and spoon into the baking dish. Sprinkle topping evenly over the apples. Bake in center of the oven for 45 minutes or until the crisp is bubbly and the apples are tender. Let cool slightly.
Adapted from Parade, October 2000 (from Epicurious.com)