If using dried chiles, bring a pot of water to a boil. Add the chiles to the pot, turn off the heat, and cover. Make sure all of the chiles are submerged in the hot water. After about 15 minutes, stir the chiles. Once the chiles are hydrated, after about 30 minutes, drain the water from the pan and set the chiles aside.
Remove the seeds and stems, and place the chiles in a blender. Set aside.
In a medium frying pan over low heat, toast the seeds. Toss every few minutes to keep from burning until they are slightly browned and fragrant, about 5 to 8 minutes.
Add the toasted seeds, garlic, lemon juice, and salt and pepper to the blender with your chiles (you can also use a small food processor, or an immersion blender with a small mixing bowl). Pulse the harissa into a paste. Use immediately and store the leftover sauce in an airtight jar in the refrigerator for up to 1 week.