Rehydrate chiles in hot water until soft. Reserve 1 tablespoon of the water. Drain them, pat dry in paper towel, toss in food processor along with peeled garlic cloves, cumin, coriander, and salt.
Whiz until they form a smooth paste. Add the reserved water and the olive oil; whiz again until blended.
Best if you let stand overnight or at least a few hours for the flavours to marry.
Store leftover in fridge in a sealed container, with a layer of olive oil on top, and use within 6 weeks.
Notes
Red New Mexico peppers work nicely. Use whatever chiles you can find -- you won't be able to get ahold of the Nabeul and Gabes peppers that are commonly used in Tunisia, anyway. But choose peppers with a very moderate heat. You may use fresh peppers if you wish -- steam or roast them first, and remove seeds. If using fresh peppers, then for the water, just use tap water in place of the soaking water. Optional: add a few sun-dried tomatoes, rehydrated.