Heat the olive oil in a large pot over medium heat. Add the diced onion and cook for 4 minutes until it softens.
Stir in the minced garlic and cook for 1 minute until fragrant.
Pour in the vegetable broth and bring the mixture to a boil.
Add the orzo and cook for 8 minutes, stirring now and then.
Add the frozen mixed vegetables and frozen spinach straight from the bags. Simmer for 5 minutes until the vegetables are heated through.
Remove the pot from the heat. Stir in the lemon zest, lemon juice, and dried oregano.
Season with salt and black pepper. Ladle the soup into bowls and top each serving with chopped fresh parsley.