Preheat oven to 375°F (190°C). In a large bowl, toss apple slices with granulated sugar, cornstarch, cinnamon, nutmeg, lemon juice, and a pinch of salt until evenly coated.

In a medium bowl, stir together oats, almond flour, brown sugar, cinnamon, and salt. Cut in cold butter until the mixture forms pea sized clumps.

Transfer apples to a 9x13 inch baking dish and spread evenly. Scatter topping over the apples. Bake 40 to 45 minutes until filling is bubbly and topping is deep golden.

Cool at least 10 minutes, then scoop into bowls and serve warm.