Heat oven to 180°C (160°C fan) and line a 20 × 20 cm (or similar) tin with parchment.
Mix flour, oats, sugar, cinnamon, and salt; stir in melted vegan butter until crumbly.
In a pan, cook apples with vegan butter, maple, cinnamon, lemon juice, and vanilla seeds (add the pod too) for 5–7 mins until just tender. Remove pod; stir in cornflour and cook 1 min to thicken.
For caramel, simmer brown sugar, vegan butter, and maple 3–4 mins until it coats a spoon. Add oat cream and a pinch of salt; simmer 2–3 mins until glossy. Stir in pecans; cool 5–8 mins until thick but pourable.
Press two-thirds of the crumble mix into the tin, using a glass or the back of a spoon to make sure it is well pressed down.
Spread apple filling over the base, drizzle half the caramel, scatter remaining crumble, and press lightly. Sprinkle the remaining crumble mix over the top.
Bake 35–40 mins until golden and bubbling at the edges. Cool completely, cut into 12 bars, and finish with the remaining caramel.