Start by chopping the carrots into 1-inch chunks, dicing the onion and celery, and mincing the garlic. These fresh ingredients will form the flavor base of your soup.
Heat the olive oil in a skillet over medium heat until it shimmers and begins to gently crackle. Add the diced onion and celery, sautéing until they become fragrant and translucent, about 5 minutes.
Add the minced garlic to the skillet and cook for another 30 seconds until fragrant, being careful not to burn it. This step deepens the aroma and flavor of the base.
Transfer the sautéed vegetables and garlic to your slow cooker. Add the chopped carrots, canned fire-roasted tomatoes with juice, vegetable broth, and fresh thyme. Stir everything together to combine.
Season the mixture with salt and pepper to taste. Cover the slow cooker with its lid, set it to low, and let it cook for 6 to 8 hours. The aroma of simmering vegetables and herbs will fill your kitchen as the flavors meld and deepen.
About 30 minutes before serving, add the green beans directly into the slow cooker. Stir gently, then continue cooking uncovered on low to allow the broth to thicken slightly and the green beans to tenderize without losing their bright color.
Check the soup’s tenderness and flavor—if the vegetables are soft and the broth has thickened slightly, it’s ready. Taste and adjust seasoning with additional salt, pepper, or a splash of lemon juice if desired.
Serve the soup hot, garnished with fresh herbs if desired. Enjoy the comforting warmth and rich aroma of this slow-cooked vegetable masterpiece.
