Preheat the oven to 450 degrees F (230 degrees C). Line a rimmed baking sheet with aluminum foil.

Place baby eggplant into a colander set over a large bowl. Sprinkle salt liberally over eggplant; let sit to drain for 30 minutes.

Toss together tomatoes, zucchini, onion, and garlic in a second large bowl. Drizzle with olive oil and toss to coat; season with salt and pepper.

Rinse baby eggplant to remove salt and pat dry with paper towels; add to tomato mixture and stir. Add more olive oil as needed to ensure eggplant is coated. Spread onto the prepared baking sheet.

Roast in the preheated oven until vegetables are tender, about 30 minutes.