Preheat the oven to 375 degrees. Grease the bottom and sides of an 8x8 inch baking dish.
Cut the apples into approximately 1 inch chunks. I didn't peel mine, but you can if it'd make you happy. Toss in a large bowl with the cranberries, sugar, lemon juice, flour and cinnamon. Spread evenly in the baking dish.
In a medium bowl, combine the rolled oats, flour, brown sugar, salt and walnuts. Use your fingers to work the butter into the topping mixture, until evenly distributed.
Sprinkle the topping mixture over the filling.
Bake the crisp for 40 minutes, or until the filling is bubbling and the topping is golden.