Heat the oil in a large saucepan over high heat. Add the onion and saute for five minutes, or until softened and translucent. Add the tomatoes, ginger and garlic and bring to a simmer. Sir in the chili, water, coffee, tamarind paste, berbere, cumin and coriander seeds and bring to a simmer. Reduce the heat and simmer for 40 minutes.
Add the honey and simmer for another 10 minutes, or until the sauce is thick enough to coat the back of a spoon. Let cool.
Store in a tightly-covered container in the refrigerator for up to five days.