Optional Flavor-Boosting Step: For an even deeper flavor, heat the olive oil in a large skillet over medium heat. Add the chopped onion, carrots, and celery and cook until the onion is softened, about 5-7 minutes. Add the minced garlic and cook for 1 more minute until fragrant. Transfer this mixture to the bottom of your slow cooker. (If you’re short on time, you can skip this step and just add the raw vegetables directly to the slow cooker).

Layer the Ingredients: Place the diced potatoes into the bottom of a 6-quart or larger slow cooker. If you skipped the sautéing step, add the chopped onion, carrots, celery, and garlic now.

Add Broth and Seasonings: Pour the undrained fire-roasted tomatoes and the rinsed kidney beans over the vegetables. Pour in the vegetable broth. Stir in the dried thyme, dried rosemary, bay leaf, salt, and pepper.

Cook Low and Slow: Stir everything gently to combine. Secure the lid on the slow cooker. Cook on LOW for 6-8 hours or on HIGH for 3-4 hours. The soup is ready when the potatoes and carrots are perfectly tender.

Add Final Vegetables: About 30-45 minutes before serving, remove the bay leaf. Stir in the frozen green beans and frozen corn. Place the lid back on and continue to cook until the frozen vegetables are heated through and tender.

Finish with Fresh Herbs: Just before serving, stir in the fresh chopped parsley. Taste the soup and adjust the seasoning if needed, adding more salt or pepper to your preference.