In small bowl, combine honey, chili flakes, lemon zest, and 1 Tbsp water. In dry medium-sized skillet over medium heat, toast sunflower seeds, pumpkin seeds, and sesame seeds, stirring often, until sesame seeds are lightly browned, about 3 minutes. Add honey mixture and cook, stirring often, until seeds stick together in small clumps and they look glazed, about 2 minutes. Scrape seed mixture onto parchment paper; let cool to harden together. Break into small clusters.