2 tablespoons olive oil, plus more for serving (optional)
1 medium red onion, chopped
2 medium carrots, peeled and diced
1 large celery stalk, diced
1/4 teaspoon red-pepper flakes
1 teaspoon minced fresh rosemary, or 1/4 teaspoon dried
Coarse salt and ground pepper
1 can (14.5 ounces) whole peeled tomatoes, drained and finely chopped
1 large potato, peeled and diced
1/4 head Savoy or green cabbage (1/2 pound), cored and thinly sliced
1 can (15 ounces) cannellini beans, rinsed and drained
1/2 pound green beans, trimmed and cut into 1-inch pieces
1 garlic clove, minced (optional)
1/4 cup thinly sliced fresh basil, plus torn leaves for serving (optional)
3/4 cup grated Parmesan, for serving