Preheat Oven: Preheat oven to 350°F (175°C) and line a 9×13-inch baking pan with parchment paper.
Mix Wet Ingredients: In a large bowl, whisk melted butter, oil, brown sugar, and granulated sugar until combined.
Add Eggs & Vanilla: Add eggs and vanilla extract, then mix until smooth.
Add Bananas & Milk: Stir in mashed bananas and milk until well combined.
Mix Dry Ingredients: In a separate bowl, whisk flour, baking soda, salt, and cinnamon.
Combine Batter: Add dry ingredients to wet mixture and mix until just combined.
Add Chocolate Chips: Fold in 1 cup chocolate chips evenly into the batter.
Transfer to Pan: Spread batter evenly into prepared baking pan.
Top with Chips: Sprinkle remaining chocolate chips on top.
Bake Bars: Bake for 25–35 minutes until edges are golden and a toothpick comes out clean.
Cool Bars: Let bars cool completely in the pan before slicing.
Slice & Serve: Cut into squares and serve.