With a small, sharp knife, cut peel and white membrane from oranges. Slice the oranges crosswise 1/8 to 1/4 inch thick and discard seeds.
In a small bowl, mix 4 tablespoons vinegar with olive oil and sugar. Stir in the spice blend.
In a wide, shallow bowl, gently mix orange slices, onions, slivered mint, and chopped cilantro. Pour in dressing and mix gently. Taste and add salt and more vinegar if desired.
Scatter olives, mint leaves, and cilantro leaves over the top. Spoon salad and dressing onto plates.
Spice blend: Combine 3/4 teaspoon cumin seeds or ground cumin, 1/2 teaspoon paprika or mild ground dried chili, 1/2 teaspoon black peppercorns or 1/4 teaspoon ground black pepper, 1/2 teaspoon kosher salt, 1/4 teaspoon chopped fresh thyme leaves, 1/4 teaspoon curry powder, and 1/8 teaspoon ground cinnamon; if using whole spices, whirl mixture in a grinder or small food processor to a powder.