Preheat the oven to 350°F (175°C). Grease an 8x8-inch baking pan with nonstick spray and set aside.
In a large bowl, combine the oats, ground cinnamon, baking powder, and salt; stir to mix evenly.
In a separate bowl, whisk together the almond milk, maple syrup, melted butter, egg, and vanilla until smooth.
Pour the wet mixture over the dry oat mixture and stir until just combined, then gently fold in 1 cup of the blueberries.
Transfer the mixture to the prepared pan and spread into an even layer. Scatter the remaining 1/2 cup blueberries and the chopped nuts on top, if using.
Bake for about 40 minutes, until the top is golden and the center is set. Let cool 5 minutes before slicing and serving warm.