Preheat your oven to 350°F (175°C).
Grease a muffin tin with cooking spray or line it with muffin liners.
In a large mixing bowl, whisk together the eggs, mashed banana, brown sugar, vanilla extract, and almond milk until well combined.
In another bowl, combine the oats, cinnamon, salt, and baking powder; mix well.
Pour the dry mixture into the wet ingredients and stir gently until just combined.
Fold in the blueberries and any additional mix-ins you desire.
Scoop the batter into each muffin cup, filling them about 2/3 full.
Bake for about 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and let them cool in the pan for about 5 minutes before transferring them to a wire rack.