Start by chopping your carrots into bite-sized pieces, then slice the zucchini and onion into similar-sized chunks.
Mince the garlic cloves finely to release their fragrant aroma.
Layer the chopped root vegetables at the bottom of your slow cooker for even cooking, then add the zucchini and sliced onion on top.
Pour in the vegetable broth, making sure the ingredients are just covered. Stir in the minced garlic, dried thyme, and tuck in the bay leaves.
If using, add the can of diced tomatoes to the mixture for an extra burst of brightness and acidity.
Cover the slow cooker with its lid and set it to low for 6 to 8 hours, or high for 3 to 4 hours, until the vegetables are tender and the broth is fragrant.
Once cooked, check that the vegetables are soft and the aroma is rich. Remove the bay leaves and taste the broth, adjusting salt if needed.
Scoop the hot stew into bowls, garnishing with fresh herbs if desired, and enjoy its rustic, comforting flavors.