Preheat oven to 375 degrees.
Wash blueberries; dry them. If you use frozen, defrost and dry off any access moisture.
Grease an 8x8 glass pan.
To the prepared blueberries, combine lemon juice, sweetener of your choice, and cornstarch. Mix together.
Spread the mixture in the greased pan.
In a separate bowl, mix all the dry ingredients together.
Cut the butter (vegan) into the dry mixture until small crumbles form. (If use coconut oil, just stir in).
Sprinkle the crumble mixture on top of the blueberries.
Bake in the oven for 25-30 minutes. It will be bubbly and crumbles will become brown and toasty.
Let cool. Serve warm or cool.
Refrigerate leftovers, covered.