Preheat your oven to 180°C (375°F) and line a baking pan (ca. 20cmx20cm) with parchment paper
In a large bowl, mix together oats, flour, sugar, baking powder and salt
Add vegan butter and mix until the dough comes together. The dough should stick together
Gently press two thirds of it onto the bottom of the prepared baking pan
Bake for ca. 10-12 minutes or until the edges just start to brown
For the jam, add 2 cups of frozen berries to a saucepan over medium heat. Add 2-3 tbsp. water and cook until berries are defrosted. Add 3 tbsp. chia seeds and 1 tbsp. lemon juice. Mash everything with a fork and cook on low heat until thick (ca. 5 minutes)
Spread your jam over the baked crust and sprinkle the remaining oat mixture over the jam
Bake for 20-25 minutes or until the top has lightly browned and the filling is bubbly
Remove from the oven and let the bars cool completely before cutting