Preheat the oven to 375°F (190°C). Butter a 9x13-inch baking dish.
Make the filling: in a large bowl, toss the sliced apples, cranberries, granulated sugar, flour, cinnamon, nutmeg, vanilla, and lemon juice until the fruit is evenly coated. Pour into the prepared baking dish and spread into an even layer.
Make the topping: in a medium bowl, stir together the oats, flour, brown sugar, cinnamon, and salt. Pour in the melted butter and stir until clumps form, then fold in the chopped pecans.
Top the fruit: sprinkle the oat topping evenly over the filling, covering it edge to edge. Leave a few chunky clumps — they bake into the crunchiest bits.
Bake: bake for 45 to 50 minutes, until the topping is deep golden brown and the filling is bubbling thickly around the edges and the apples are tender when pierced with a knife.
Rest and serve: let the crisp rest for 15 minutes so the juices thicken. Serve warm with vanilla ice cream or a dollop of whipped cream.