In a large skillet, lightly toast the pumpkin seeds over medium-low heat, stirring frequently, for about 10 minutes. Let cool.
In a microwavable bowl, melt the chocolate in a microwave oven at 50 percent power, stirring at 30-second intervals until just melted, about 3 minutes. Stir in the chili powder, then 1 3/4 cups of the toasted pumpkin seeds until evenly coated.
Spread the chocolate mixture on a wax paper-lined baking sheet in an even 1/4-inch-thick layer. Sprinkle on the remaining toasted pumpkin seeds.
Refrigerate the chocolate until set, about 30 minutes, then break into pieces. Makes 1 1/4 pounds.