Line an 11″ x 17″ baking sheet with parchment paper. Combine pistachios, dried cherries, and pumpkin seeds in a bowl. Set aside 1/2 cup of mixture.To temper chocolate: Using a microwave, place 3/4 of chocolate in a microwave-safe glass or ceramic bowl (set aside remaining chocolate). Program microwave at 50 percent power. With bowl uncovered, heat chocolate for 30 seconds and then stir with a rubber spatula. Repeat, heating for 30 seconds and then stirring, until almost all the chocolate in the bowl is melted, about 4 minutes total.Using an instant-read thermometer, check temperature of chocolate. It should be no more than 115°. If it hasn’t reached desired temperature, continue to heat (in 10-second increments). Then add reserved chocolate and stir constantly until completely melted and smooth and thermometer reads 88° to 90°. Chocolate is now tempered.Stir nut mixture into bowl containing chocolate.Using an offset spatula, spread chocolate in an even layer, about 1/4 inch thick, on the parchment. Sprinkle with reserved 1/2 cup nut mixture. Allow bark to cool until hard, at least 20 minutes. Break into irregular pieces.