2 tablespoons olive oil, divided

1 yellow onion, diced

1 teaspoon salt, divided

1 teaspoon freshly cracked black pepper, divided

3 garlic cloves, minced

4 cups chicken broth

1/2 cup chopped carrots

1 cup chopped zucchini (about 1 medium)

1/2 cup frozen peas

1/2 cup frozen green beans

1/4 cup frozen corn

1 stalk celery, sliced

1 (14.5-ounce) can diced tomatoes

1 teaspoon Italian seasoning

1 pound lean ground chicken

1/3 cup plain Panko breadcrumbs

1/4 cup freshly grated Parmesan cheese (plus more for serving)

1 large egg

2 1/2 tablespoons chopped fresh flat-leaf parsley (for serving)

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Heat 1 tablespoon olive oil in a skillet over medium-high heat. Add onion, 1/4 teaspoon each of salt and pepper, and cook 6 minutes until soft and golden. Stir in garlic and cook 1 more minute.
Transfer half of the onion mixture to a large mixing bowl for the meatballs and add the remaining half to the slow cooker.
To the slow cooker, add chicken broth, carrots, zucchini, peas, green beans, corn, celery, diced tomatoes, 1/4 teaspoon each of salt and pepper, and Italian seasoning. Stir to combine.
In the mixing bowl with the reserved onion, add ground chicken, breadcrumbs, Parmesan, egg, and the remaining salt and pepper. Mix gently until just combined.
Shape into 1 1/4-inch meatballs.
Heat the remaining 1 tablespoon olive oil in the same skillet and brown meatballs on all sides, about 5–6 minutes. Do not fully cook through.
Transfer meatballs to the slow cooker, nestling them gently into the soup without stirring.
Cover and cook on HIGH for 3–4 hours, or LOW for 6–7 hours, until meatballs are fully cooked (165°F internally) and vegetables are tender.
Before serving, top with fresh parsley and extra Parmesan.

For extra depth, add 1 tablespoon tomato paste or a pinch of red pepper flakes.

Use ground turkey instead of chicken for a flavorful variation.

Skip the Parmesan for a lighter or dairy-free version.

For a heartier soup, stir in cooked pasta, rice, or quinoa before serving.

Use fresh vegetables instead of frozen for a more rustic texture.