Preheat the oven to 375° F. Spray a baking dish with oil.
Wash and slice 6 cups of peaches and place them in the bottom of a greased baking dish.
Sprinkle the sliced peaches with 2 tablespoons of sugar, 1 tablespoon of cornstarch, and 1 teaspoon of cinnamon.
Stir the peaches gently until they are evenly coated in the sugar mixture.
Make the crumble topping
Place 1/3 cup vegan butter, 3/4 cups flour, 3/4 cups oats, 1/4 cup brown sugar, 1/2 tsp cinnamon, 1/8 tsp salt, and 1/8 tsp baking soda in a mixing bowl.
Mix well until the butter is incorporated and you have a uniform crumbly mixture. (I find it easiest to use my hands for this step, but you can use the back of a fork or a pastry cutter.
Sprinkle the crumble mixture evenly on top of the sliced peaches.
Bake at 375° F for 30 minutes or until the top is crispy and slightly darker.
Let it cool for about 15 minutes before serving to let it firm up a little.