In a medium bowl, mix peanut butter, oats, honey, and vanilla extract until combined.
Line a muffin tin with liners and divide the oat mixture evenly into 10 muffin slots. Press down firmly.
Freeze for at least 2 hours until solid.
In a small saucepan, melt dark chocolate chips and coconut oil over low heat, stirring until smooth.
Pour the melted chocolate over each oat cup, spreading evenly. Sprinkle flaky salt if desired.
Freeze for another 30 minutes until the chocolate sets.
Enjoy straight from the fridge or freezer!