Arrange the eggplant slices in 1 layer onto a baking sheet. Drizzle with olive oil and roast until they are soft and pliable, about 15 to 20 minutes, turning them half way through the cooking time. Reserve the 4 largest rounds and finely chop the remaining eggplant.
Heat a large skillet over medium-high heat. When hot, add the onions and season with salt. Cook until soft, about 5 minutes. Put the cooked onion and chopped eggplant in a large bowl. Add the feta, bread crumbs, kasseri, lemon zest, oregano, crushed red pepper, and garlic. Add 2 to 3 tablespoons olive oil and combine well. Taste and adjust the seasoning, if needed.
Divide the filling among the 4 reserved eggplant rounds. Roll the eggplant around the filling and arrange on a serving platter with the seam side down.
Combine the yogurt and mint together in a small bowl. Garnish each eggplant roll with a dollop of yogurt and serve at room temperature. OPAH!!!