Roast the peppers and eggplant over charcoal or gas flame, or bake in a preheated oven at 250ºC until the skins are blistered and black.
Place the roasted vegetables in a paper bag and let them steam in their own heat for 10 minutes. Peel off and discard the burnt skins along with the stems and seeds.
Mash the pepper and eggplant pulp together to form a homogeneous mass, either smooth or slightly chunky, as desired.
Heat 3 tablespoons oil in a large skillet and saute the onion until very soft. Add the garlic and cook 2 minutes longer. Remove from heat and stir in the pepper, eggplant pulp, mixing well.
Slowly drizzle remaining oil into the mixture, stirring constantly to incorporate all the oil.
Add lemon juice and vinegar, salt and pepper to taste.
Transfer to a serving bowl and garnish with parsley.
Serve as an appetizer spread on thick slices of country-style white bread, or flat pita bread, or use as a side dish to accompany grilled or roasted meats.