Preheat the oven to 350°. To a rimmed baking sheet, add the onion flakes, garlic powder, poppy seeds, sesame seeds and sea salt and give the pan a few gentle shakes to evenly disperse the spices. Bake until golden brown and toasted, 4 to 5 minutes. Remove from the oven and turn out onto a large plate to cool, then store in an airtight container or glass jar at room temperature for up to 3 months.