Insert metal grilling skewer tip or marshmallow stick into one flat end of marshmallow, being careful not to pierce through the other end.
Roast marshmallows over open flame by allowing the marshmallow to flame briefly to char. Blow out flame.
Cool marshmallows briefly, then carefully remove blackened exterior shell from roasted marshmallows. Set shells on large plate with the open side up. (Note: continue grilling interior of marshmallows to eat and enjoy immediately!)
Fill a large resealable plastic bag with whipped cream. Close top and snip 1⁄2" off corner of bag. Use as a pastry bag to fill each marshmallow shell with about 2 Tbsp. whipped cream mixture. Sprinkle with cinnamon and top each cream filled shell with 1 whole strawberry.