Combine ground beef, bread crumbs, egg, minced garlic, crushed fennel seeds, chopped thyme, salt, and pepper in a large mixing bowl.
Shape the mixture into small, uniform meatballs about one inch in diameter and place them on a baking sheet or plate.
Heat a skillet over medium-high heat, add a splash of oil, and brown the meatballs for 2-3 minutes on each side until they develop a light golden crust. This step adds flavor and helps them hold together in the slow cooker.
Transfer the browned meatballs to the slow cooker, along with chopped onion, sliced carrots, diced tomatoes with juice, and green beans.
Pour the broth over the ingredients in the slow cooker, ensuring everything is submerged or well-coated in liquid.
Season the broth with additional salt, pepper, and fresh thyme, then cover the slow cooker with its lid.
Set the slow cooker to low and cook for 4 hours, letting the flavors meld and the meatballs become tender.
Once cooking is complete, gently stir the soup to distribute the flavors and check if the vegetables are tender and the meatballs are cooked through.
Taste the broth and adjust seasoning as needed, adding more salt, pepper, or herbs for a personalized touch.
Serve the warm soup in bowls, garnished with extra fresh thyme or herbs if desired, and enjoy the hearty, aromatic flavors of autumn.
