Place 1 tablespoon olive oil into the slow cooker. Add the chopped onion, diced carrots, diced celery, and minced garlic. Toss lightly so the oil coats the vegetables.

Pour in 6 cups of broth, then add the 2 cups diced tomatoes, 1 cup trimmed green beans, and 1 cup diced potatoes. Sprinkle in 1 teaspoon dried thyme, 1 teaspoon dried basil, and salt and pepper to taste.

Stir everything gently to combine, ensuring ingredients are evenly distributed.

Cover and cook on low for 6–8 hours or on high for 3–4 hours, until the potatoes are tender and the flavors have melded.

If using cooked chicken or canned beans, stir them in during the last hour of cooking.

Taste the soup and adjust salt and pepper before serving. For a brighter finish, squeeze a little lemon juice or add fresh chopped parsley.