Place apple slices in a 2-quart square baking dish, set aside. Stir together in a small bowl, 2 tablespoons flour and 1 tablespoon brown sugar until well mixed. Sprinkle over apple slices in dish, toss to coat.
Bake, covered in a 375 degree oven for 15 minutes. Meanwhile, in a medium bowl combine rolled oats, 2 tablespoons flour and 2 tablespoons brown sugar. Using a fork, stir in peanut butter until mixture resembles coarse crumbs. Stir in peanuts.
Uncover apple mixture, sprinkle with oat mixture. Bake, uncovered, for 15 to 20 minutes more or until apples are tender and topping is golden.