Over low heat, warm the seeds until they are aromatic, approximately 5 minutes. Don't let them burn.
Using a mortar and pestle, crush the seeds, along with the mint, sea salt, and dried chilies into a coarse powder.
Transfer the powder to a sealable jar and add in the smashed garlic and olive oil. Allow, the spices to settle to the bottom, then seal the jar.
Let the oil infuse with the spice flavors for 24 hours prior to use.
Notes
You can use many different types of chilies in harissa to create unique flavors for your oil. - Ancho chilies: Mild and slightly smoky - Guajillo chilies: Mild and sweet - Chipotle chilies: Medium and smoky - Thai chilies: Hot and earthy