Wash your hands well with soap and warm water for at least 20 seconds.
Peel and cut onion into medium pieces.
Peel and mince garlic.
Wash eggplant, zucchini, yellow squash, and tomato and cut into medium pieces. Set tomato pieces aside.
In a medium bowl, add onion, eggplant, zucchini, squash, garlic, oil, basil, oregano, salt, and pepper. Toss until vegetables are well coated.
Coat baking sheet with non-stick cooking spray. Spread vegetables out in a single layer. Bake for 20 minutes. Remove from oven.
Add diced tomato to baking sheet. Return the baking sheet to oven. Bake, stirring occasionally, until vegetables are golden crisp, about 15–20 minutes.