Heat oven to 375 degrees. Toss fruit with half the cinnamon and 2 tablespoons sugar, and spread it in a lightly buttered 8-inch square or 9-inch round baking pan.
Combine remaining cinnamon and sugar in container of a food processor with butter, oats and nuts; pulse a few times, just until ingredients are combined. (Do not purée.) To mix ingredients by hand, soften butter slightly, toss together dry ingredients and work butter in with fingertips, a pastry blender or a fork.
Spread topping over apples, and bake about 40 minutes, until topping is browned and apples are tender. Serve hot, warm or at room temperature.