Heat the olive oil in a large nonreactive skillet. Add the onion and cook over high heat, stirring frequently, until softened and lightly browned around the edges, 3 to 5 minutes. Stir in the cumin and turmeric to lightly coat the onion. Add the tomato puree, reduce the heat to low and simmer, covered, until slightly thickened, 12 to 15 minutes. Stir in a little water if the sauce is too thick. Add the eggplant, sugar, 1 teaspoon salt and a pinch of cayenne. Cover and cook over low heat for 10 more minutes. Season with salt and cayenne, garnish with cilantro and serve with lemon wedges.