Preheat oven to 425F. Line a 12-cup muffin tin with muffin liners and set aside.
Place oats in a medium nonstick pan and set over medium heat. Stir oats around 4-6 minutes until fragrant and a light golden brown. Pulse oats in a food processor several times until finely chopped or finely chop with a knife. Set aside.
In a large bowl, beat butter and sugars until smooth and creamy. Beat in eggs, banana, milk, and vanilla until smooth.
In a separate medium bowl, combine flour, cinnamon, baking powder, baking soda, and salt. Fold into liquid mixture with oats and chocolate until batter is just combined. Fill muffin cups to brim with batter and set aside for a moment.
Streusel Topping
In a small bowl, combine all streusel ingredients until crumbly. Sprinkle evenly over muffin batter, pressing lightly to adhere crumbs. Top with additional chocolate chunks or chips if desired.
Bake muffins at 425F 5 minutes, then reduce heat to 375F and continue baking an additional 10-15 minutes until a toothpick inserted in center of muffin comes out clean.
Cool muffins 20 minutes in pan, then transfer to a wire cooling rack to cool completely. Enjoy!
Notes
Storing InstructionsStore muffins in an airtight container at room temperature up to 4 days.