In a large skillet, heat ¼ cup oil over medium-high heat until shimmering. Meanwhile, place flour in a shallow bowl.

Working in batches, lightly dredge eggplant slices in flour, shaking off excess. Add dredged eggplant to the hot oil and fry until deeply golden brown on both sides, 1 to 2 minutes per side. Transfer to a paper towel-lined plate and sprinkle with ¼ teaspoon salt. Repeat with remaining oil, eggplant, and salt, heating each addition of oil until shimmering before adding the next batch; set aside.

Add bell peppers and chiles (if using), to the remaining hot oil and cook until slightly softened but still bright green, about 1 minute. Transfer to paper towel-lined plate; set aside.

In a medium saucepan, heat oil over medium heat until shimmering. Add garlic and cook, stirring constantly, until fragrant, about 30 seconds. Add vinegar and cook until slightly reduced, about 30 seconds.

Stir in passata or tomato purée, tomato paste, and ¼ cup (60 ml) water, salt, cumin, Vegeta (if using), sugar (if using), and black pepper. Bring to a simmer, then reduce heat to low and cook, stirring occasionally, until flavors meld and sauce has slightly thickened, about 20 minutes.

While sauce is cooking, adjust oven rack to middle position and preheat oven to 375°F (190°C). Once sauce is off the heat, add eggplant, bell peppers, and chiles to tomato sauce and gently toss until lightly coated.

Transfer eggplant mixture to a 9 x 13-inch (23 x 33 cm) baking dish and bake until the sauce is bubbling and the vegetables are heated through, 20 to 25 minutes.

Let cool for 10 minutes. Serve hot, warm, or at room temperature with pita bread, if desired.