Melt the chocolate in a double boiler over simmering water until smooth, or melt in the microwave in a 2 quart glass dish. Microwave on high(100%) for 1 minute, stir, and microwave on high for 1 minute more. If necessary, microwave for 10 seconds more, and stir until the chocolate is melted and smooth. Stir in the pretzel pieces, nuts and M&M's. Stir will with a flexible spatula.