In a large saucepan or stock pot, heat the oil over medium heat until shimmering. Add the onion, mushrooms, salt, and pepper and sauté until vegetables are tender, about 7 minutes. Add the garlic and cook another minute. Stir in the chicken broth, basil and oregano. Bring to just a boil and then reduce the temperature and simmer 10 minutes. Add the cauliflower rice and the meatballs and cook until the meatballs are cooked through and float to the top, about 5 minutes. Add the spinach leaves and cook until wilted, 2 minutes more. Season to taste