Preheat oven to 350°F. Line a 9x13-inch pan with parchment and lightly grease.
Mash bananas in a bowl until mostly smooth with a few small chunks.
Whisk melted butter, granulated sugar, and brown sugar until glossy and combined.
Whisk in beaten eggs and vanilla until the mixture looks slightly thick and uniform.
In a separate bowl, whisk flour, cinnamon, baking soda, and salt to blend evenly.
Stir dry ingredients into the wet mixture just until a few streaks remain.
Fold in mashed bananas and chocolate chips until no dry pockets remain. Do not overmix.
Spread batter into the pan and smooth the top. Bake 22–27 minutes until set and a tester has a few moist crumbs.
Cool in the pan on a rack, then lift out, slice into squares, and serve.