Line a 9×13 pan with parchment paper or foil. Place pretzels side by side all over the bottom of the pan. I make one layer, but if you want more pretzel chunks you could certainly use more. Melt chocolate in the microwave in 30-second increments until completely smooth. Completely cover pretzels with melted chocolate, then lightly scatter mini M&M’s across surface of chocolate. Refrigerate to harden. Cut or break into pieces once firm.