Heat olive oil in a large pot over medium heat. Add the onion and garlic and sauté until the onion is translucent, about 5 minutes.
Add the butternut squash and carrots to the pot, cooking for another 3 minutes.
Stir in the barley, vegetable broth, salt, pepper, and thyme. Bring to a boil.
Reduce the heat to low, cover, and let simmer for 25 minutes until barley is tender.
Add the frozen peas and cook for an additional 5 minutes, until the peas are heated through.
Serve hot, garnished with fresh herbs if desired.