Heat olive oil in a large pot over medium heat.
Add diced onions and sauté until translucent, about 5 minutes.
Stir in minced garlic and cook for an additional minute.
Pour in vegetable broth and bring to a simmer.
Add diced carrots and celery, cooking for 5-7 minutes until tender.
Stir in orzo pasta and cook according to package instructions, about 8-10 minutes.
Once the orzo is al dente, stir in lemon juice and thyme.
Season with salt and pepper to taste.
Remove from heat and let the soup sit for a few minutes to allow flavors to meld.
Serve hot, garnished with fresh parsley.