Preheat your oven to 350 degrees F, lightly oil a baking dish, then put it aside.
Add blueberries into a large mixing bowl. Add in the chopped apples, sugar, lemon juice, cornstarch, vanilla and cinnamon and combine by stirring all ingredients.
Combine the flour, oats, brown sugar and salt in a medium bowl. Add the melted butter over the oat mixture and stir to combine.
Pour the blueberry mixture into the baking dish, spread then top with scattered oat mixture.
Bake for about 45 to 55 minutes or until the top layer looks firm and golden and the fruit juices begin to bubble.
Let it sit on a wire rack for a minimum of 15 minutes before you serve it. Enjoy!
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