Heat the olive oil in a large pot or dutch oven over medium heat.
Add the diced onion, carrots, and celery. Sauté for 5-7 minutes until the onions are translucent and vegetables begin to soften.
Stir in the minced garlic and dried thyme (if using), cooking for another 1 minute until fragrant.
Pour in the vegetable broth and bring the mixture to a boil.
Stir in the orzo pasta and reduce heat to a simmer. Cook for 8-10 minutes, or until the orzo is al dente.
Remove the pot from the heat.
Stir in the fresh lemon juice, lemon zest, and chopped fresh dill.
Season with salt and freshly cracked black pepper to taste.
Serve immediately, garnished with extra dill and lemon slices if desired.