Line an 8x8 inch pan with foil or parchment paper and lightly grease the liner.
In a large pot over medium heat, melt butter.
Stir in corn syrup, 1/2 cup sugar, marshmallows, vanilla, salt, and 1/2 teaspoon cinnamon.
Continue to stir until marshmallows are completely melted and incorporated.
Stir in rice cereal.
Transfer rice cereal mixture to prepared pan. Gently pat into an even layer with a rubber spatula or greased fingertips - be cautious not to press down to much as this will harden the bars.
Combine chocolate chips and oil in a microwave safe bowl. Microwave on half power for 25 seconds at a time until softened, then stir til smooth. Spread over bars.
Stir together cinnamon and sugar. Immediately sprinkle over melted chocolate.
Allow to cool until chocolate is firm (putting the pan in the fridge or freezer for a few minutes will speed this up!). Cut into bars and serve or store in airtight container up to 1 week.