Combine 1 Tbsp. olive oil, soy sauce, cumin and cayenne. Lightly coat both sides of eggplant slices with mixture. Discard outside skin-covered slices. Grill eggplant 2 to 3 minutes per side; set aside. Shape pizza dough into 2 9-in. rounds. Brush each with 1 Tbsp. olive oil. Layer with onions then grilled eggplant. Bake at 500 degrees F until crusts are golden, about 8 minutes. Slice pizzas, then top with cilantro and spinach. Garnish with sun-dried tomato. Serve with oil and vinegar on side, if desired.