¼ cup extra-virgin olive oil, plus extra for serving
1 eggplant (about 1 pound), cut into 1-inch chunks
1 (28-ounce) can whole tomatoes, drained, tomatoes chopped medium, and juice reserved
1 onion, minced
1 red bell pepper, stemmed, seeded, and cut into 1-inch chunks
4 garlic cloves, minced
1 tablespoon tomato paste
1 tablespoon minced fresh oregano or 1 teaspoon dried
3 cups vegetable broth, plus extra as needed
1 pound Yukon Gold potatoes (about 2 medium), peeled and cut into ½-inch pieces
2 zucchini (about 1 pound), quartered lengthwise and sliced 1 inch thick
2 tablespoons chopped fresh basil
Salt and pepper
Grated Parmesan cheese, for serving
1. Heat 2 tablespoons oil in 12-inch skillet over medium-high heat until shimmering. Brown eggplant lightly on all sides, 5 to 7 minutes; transfer to slow cooker.
2. Heat remaining 2 tablespoons oil in skillet over medium-high heat until shimmering. Add tomatoes, onion, bell pepper, garlic, tomato paste, and oregano and cook until dry and beginning to brown, 8 to 10 minutes. Stir in 1 cup broth, scraping up any browned bits; transfer to slow cooker.
3. Stir reserved tomato juice, remaining 2 cups broth, and potatoes into slow cooker. Cover and cook until vegetables are tender, 4 to 6 hours on low.
4. Stir in zucchini, cover, and cook on high until tender, 20 to 30 minutes. (Adjust stew consistency with additional hot broth as needed.) Stir in basil, season with salt and pepper to taste, and serve with Parmesan and additional olive oil.