Preheat oven to 350°F (175°C). Lightly butter a 9x9-inch square ceramic baking dish or a 10-inch enameled cast-iron skillet.

Prepare the apple filling: In a large mixing bowl, toss the sliced Honeycrisp and Granny Smith apples with lemon juice, maple syrup, cornstarch, ground cinnamon, nutmeg, and vanilla bean paste until every slice is evenly glistening with warm spices.

Transfer the spiced apples into the prepared baking dish, pressing them down gently into an even, compact layer.

Make the crunchy streusel: In a medium bowl, whisk together the rolled oats, flour, packed dark brown sugar, chopped pecans, cinnamon, and fine sea salt. Add the cold cubed butter.

Using a pastry cutter or your fingertips, quickly work the cold butter into the dry oat mixture until crumbly pea-sized clusters and buttery nuggets form. Keep the butter cold so it creates distinct crunchy clusters during baking rather than a flat paste.

Evenly scatter the crunchy oat pecan streusel across the apple layer, ensuring edge-to-edge coverage.

Bake at 350°F (175°C) for 35 to 40 minutes, until the oat topping is deeply golden-brown and fragrant, and thick amber apple juices are bubbling vigorously along the edges of the dish.

Remove from oven and let rest for 10 minutes to allow the bubbling cinnamon juices to thicken into a glossy sauce. Spoon warm into shallow bowls and crown immediately with a generous scoop of cold vanilla bean ice cream and salted caramel drizzle.