Preheat the oven to 350F
Peel and cube apple and add to mixing bowl with 100 g brown sugar, 31 g flour, 1 tsp cinnamon, nutmeg, salt, lemon juice, and 1 tsp vanilla. Toss to combine so all apple pieces are coated
Transfer apple mixture to a 9×13 dish sprayed with nonstick spray and smooth down
Combine 125 g flour, roled oats, 200 g brown sugar, and 1 tsp cinnamon to a mixing bowl and mix together. Then add in the melted vegan butter and 1 tsp vanilla, and stir. Use your fingers to spread the topping over the apple layer, crumbling with your fingers until it is evenly spread across the top
Place in the oven for 50 minutes until the top is nicely golden and the apple mix is bubbling up the sides
Allow to cool for 10 minutes before serving