Prepare. Preheat your oven to 375f. Prep your baking pan for nonstick.
Blueberries. Place a cup and a half of the blueberries into a medium size bowl. Sprinkle a half tablespoon of flour over the blueberries and toss. Then repeat this process again.
Dry Ingredients. In a medium bowl, use a whisk to combine together the flour, baking powder, and baking soda.
Wet Ingredients. In another mixing bowl, use a whisk to combine together the oat milk, vinegar, and vanilla extract.
Combine. In a large mixing bowl, whisk or beat together the sugar and oil until well combined. Then add the ingredients from the bowl with the wet ingredients to the large mixing bowl until just combined. Add the dry ingredients to the bowl and mix until just combined.
Blueberries. Use a rubber spatula or similar item to scrape down the sides of the mixing bowl and then fold in the blueberries that were tossed with flour in the second step.
Transfer. Evenly transfer the batter to your prepared baking pan. Gently tap the bottom of the pan on your countertop to help to help even out the batter and remove any air bubble. Press the remaining blueberries into the top of the batter in the pan.
Topping. In a clean bowl, combine together the crumble topping ingredients until somewhat crumbly. Sprinkle the combined ingredients over the cake batter in the pan.
Bake. Bake the cake for 45-55 minutes or until a toothpick comes out clean when inserted into the center. The baking times can vary depending on the size of the pan you are using.
Cool. Allow the cake to cool and set for about 20 minutes before serving.