Lay frozen cinnamon rolls on parchment paper to allow them defrost for 45 minutes, no longer. Slice into 4 equal pieces, each one.
On a shallow plate combine sugar, cinnamon, (and 1 tbsp cocoa if you want it chocolate). Spray inside of bundt pan well with non stick spray. Dip and coat each cut roll in the sugar mixture.
(if making chocolate version sprinkle 1/2 cup chips in very bottom of pan first) Put coated pieces into bundt pan so they're evenly spread out. Melt butter with brown sugar, stir and pour on the top.
Cover pan with plastic wrap and a towel. Put into a warm place (in colder months place into oven with just the oven light on). Allow to rest for 1 hour.
Preheat oven to 350 degrees F. Remove towel and plastic wrap. Put filled bundt pan with risen rolls into oven on 2nd to lowest rack in oven and bake for 40 minutes or until middle is no longer sticky when toothpick or knife is inserted.
Remove and sit on cooling rack for 15 minutes. Place a plate on top and flip pan upside down so bundt slides out. Serve as is or with a tub of melted frosting poured over the top.