Preheat oven to 375°. Line muffin tins with liners if not using silicone baking pans.
In a large bowl or stand mixer, beat softened butter and brown sugar until well blended. Add in peanut butter, mashed bananas, eggs, milk, and vanilla extract. Mix on medium speed until well combined.
Stir in flour, oats, baking soda and powder, and salt. Stir just until combined. Stir in chocolate chips. Scoop batter equally into muffin pans. Bake for 18-23 minutes, or until toothpick comes out clean. Cool and enjoy!
Chopped walnuts would be a great addition to these muffins!