Preheat the oven to 350 ºF spray an 8×8 or 9x9 inch square baking dish with olive oil or avocado oil. Try to keep the baking dish as close as possible in size for the best outcome.
In a large bowl, whisk or stir the old fashioned oats, cinnamon, chopped walnuts, sliced almonds, brown sugar, vanilla protein powder of choice and salt until combined.
In a separate bowl, whisk together the eggs, almond milk, vanilla extract, maple syrup.
Pour the wet ingredients into the oat mixture and stir to combine. Gently fold in the blackberries. Pour the mixture into the baking dish and spread it evenly using a spatula.
Bake for 40-45 minutes or until golden brown on the edges and middle is no longer jiggling.
Remove from the oven and let it cool for 10 minutes, this helps the baked oatmeal stick together more.
When ready to serve, gently scoop out into a bowl or plate. It will be a tad crumbly but I prefer it this way, it feels more like a decadent treat. Serve with extra blackberries if desired.