Preheat the oven: 350°F (175°C). Line a baking sheet with parchment paper.
Mash the bananas: In a large bowl, mash until smooth.
Mix wet ingredients: Stir in melted coconut oil, sugar, and egg (if using).
Add dry ingredients: Fold in oats, flour, baking soda, cinnamon, and salt until dough forms.
Add mix-ins: Gently stir in chocolate chips or nuts if desired.
Shape cookies: Scoop 2 tablespoons of dough per cookie and flatten slightly on the baking sheet.
Bake: 10–12 minutes, until edges are golden but centers remain soft.
Cool: Let cookies cool for a few minutes on the sheet, then transfer to a wire rack. Enjoy warm or store for later.