Put all the dried chiles in a bowl and pour boiling water over them so they’re fully submerged. Soak for 10 minutes. Remove them from the water and transfer to a food processor.
Meanwhile, in a small saucepan over low heat, gently heat the unpeeled garlic cloves and olive oil for 20 minutes. Turn off the heat and let the oil cool.
Meanwhile, toast the peanuts in a dry pan until fragrant, 6 to 10 minutes, then roughly chop them. Add them to the chiles in the food processor.
Squeeze the garlic out of the skins and add it to the food processor, along with 5 tablespoons of the oil, the sugar, lime juice and zest, thyme and salt and pepper to taste. Pulse the mixture about six times until you reach a coarse consistency. Taste and add more salt if needed.
Transfer the salsa to a sterilized jar and store in the refrigerator for up to three weeks.
Preheat the oven to 355°F.
Place the unpeeled plantains in a baking dish and roast until the skins are black and the insides are completely soft, 20 to 30 minutes.
Slit the roasted plantains lengthwise. Spoon 3 tablespoons of salsa onto each plantain, crumble feta over the top and serve with lime wedges on the side.