In a large mixing bowl mash one ripe banana using a potato masher or fork. Then mix together the mashed banana, honey, vanilla, salt, and cinnamon.
Add in the oats and walnuts and mix until well combined.
Prepare a 12-cup muffin tin by spraying the cavities evenly with cooking spray.
Evenly divide the oatmeal mixture across the tin. Using your fingers, press the mixture to form cups.
Place the tin in the refrigerator for 1 hour and then bake them for 30 minutes at 350 degrees F. Allow cups to cool before removing them.
Top the cups with fresh berries and yogurt when serving.