Prep the air fryer and dish: Preheat your air fryer to 350°F (175°C) for 3–5 minutes. Use a heatproof 6–7 inch round baking dish or two smaller ramekins that fit in your air fryer basket. Lightly grease the dish.

Mix the fruit: In a bowl, combine the diced apples and strawberries with lemon juice, vanilla, granulated sugar, cornstarch, 1/2 teaspoon cinnamon, and a pinch of salt. Toss until the fruit is evenly coated and glossy.

Make the crumble topping: In a separate bowl, combine oats, almond flour (or all-purpose flour), brown sugar, remaining 1/2 teaspoon cinnamon, and a pinch of salt. Add the cold butter pieces and rub them into the dry ingredients with your fingers until the mixture forms pea-sized crumbs. If using nuts, fold them in now.

Assemble: Pour the fruit mixture into the prepared baking dish. Sprinkle the crumble topping evenly over the fruit, leaving a few small gaps so steam can escape.

Air fry: Place the dish in the basket and cook at 350°F (175°C) for 15–20 minutes, until the topping is golden and the fruit is bubbling around the edges. If the top browns too quickly, lower to 320°F and continue until the fruit is tender.

Check doneness: Insert a fork into an apple piece to ensure it’s soft. Frozen strawberries may extend the cook time by 2–4 minutes. If needed, tent loosely with foil for the last few minutes to prevent over-browning.

Rest and serve: Let the crumble stand for 5–10 minutes so the juices thicken. Serve warm with a scoop of ice cream or a spoonful of yogurt.