• Heat the olive oil in a Dutch oven or heavy-bottomed pot over medium heat. Add the onion and garlic, and sauté until the onion is softened.
• Add the eggplant, zucchini, yellow squash, and red bell pepper to the pot, stirring to combine. Cook the vegetables for 5-7 minutes until they are slightly softened.
• Add the diced tomatoes, tomato paste, thyme, oregano, salt, and black pepper to the pot. Stir everything together.
• Bring the mixture to a simmer, then reduce the heat to low and let the ratatouille cook for 30-40 minutes, stirring occasionally, until the vegetables are tender.
• Adjust seasoning to taste, then serve the ratatouille with fresh basil on top.

Slow Cooker Instructions (optional):

• If you prefer to use a slow cooker, you can follow the same steps above until step 3. Then, transfer everything to your slow cooker and cook on low for 6-8 hours or on high for 3-4 hours. Once the ratatouille is cooked, adjust seasoning to taste and serve as directed above.