Heat the olive oil in a large skillet over medium heat until shimmering. Add the diced onion and cook, stirring occasionally, until translucent and fragrant, about 5 minutes.
Add the minced garlic and cook for 30 seconds until it becomes aromatic, being careful not to burn it.
Introduce the sliced zucchini and cubed eggplant into the skillet. Cook, stirring occasionally, until the vegetables start to soften and turn lightly golden around the edges, about 8 minutes.
Add the julienned bell pepper and cook for another 5 minutes, allowing it to soften and release some of its juices.
Stir in the chopped tomatoes along with thyme and oregano. Let the mixture simmer gently, uncovered, for about 15-20 minutes, stirring every few minutes until the vegetables are tender and the flavors meld together.
Season with salt and pepper to taste, adjusting the seasoning as needed. Continue cooking for another 5 minutes until the sauce thickens slightly and the vegetables are perfectly cooked through.
Remove from heat and let sit for a few minutes to develop flavors. Serve the ratatouille warm, garnished with fresh herbs if desired.