Toast pistachios in a dry skillet over medium-low heat, stirring occasionally, until golden brown, about 6 minutes. Transfer to a small plate and let cool. Add sesame seeds, coriander seeds, cumin seeds, fennel seeds, and peppercorns to same skillet. Toast, stirring often, until fragrant, 1-2 minutes. Transfer spices to plate with nuts and let cool. Transfer nut and spice mixture and 1 teaspoon salt to a food processor or a mortar and pestle and coarsely grind. DO AHEAD: Dukkah spice blend can be made 1 week ahead. Store airtight at room temperature.