Heat olive oil in a large pot over medium heat.
Add diced onion and cook until soft and translucent.
Stir in garlic and cook for 20–30 seconds until fragrant.
Add tomato paste and water. Stir to combine and loosen the pot.
Pour in chicken broth and stir well.
Add carrots, potatoes, thyme, rosemary, and parsley.
Season with salt and black pepper.
Bring to a gentle simmer and cook until vegetables are tender, about 30 minutes.
Stir in cooked chicken and frozen peas.
Simmer for 5–10 minutes until heated through.
(Optional) Mix cornstarch with water and stir into stew. Cook 1–2 minutes until thickened.
Taste and adjust seasoning before serving.