Minestra Maritata (Italian Wedding Soup)

Ingredients

• tablespoons extra-virgin olive oil, divided
• chopped yellow onion
• chopped carrot
• chopped celery
• tablespoons minced garlic
• unsalted chicken broth
• ounces orzo, preferably whole-wheat
• tablespoons chopped fresh oregano
• teaspoon kosher salt
• cooked chicken meatballs , such as Easy Chicken Meatballs
• baby spinach
• grated Parmesan cheese