Melt 2 tablespoons of butter in a large skillet over medium heat.
Add the onions and carrots and sauté for 3-4 minutes until slightly softened.
Stir in the garlic, rice, and orzo, and cook for 2-3 minutes, stirring constantly, until the edges turn golden brown.
Pour in the chicken broth, lemon juice, lemon zest, thyme, salt, and pepper.
Bring the mixture to a boil, then reduce the heat to low.
Cover and simmer for 15-20 minutes, until the liquid is absorbed and the rice is tender.
Turn off the heat and let the pilaf rest, covered, for 10 minutes.
Fluff in the remaining butter and chopped parsley with a fork before serving warm.