Preheat your oven to 375°F. Heat olive oil in a large skillet over medium heat.
Sauté onion and celery for 3-4 minutes until softened.
Add flour and stir to coat veggies. Slowly whisk in broth and milk until smooth.
Toss in salt, pepper, garlic powder, and thyme. Stir and let it simmer for 5 minutes.
Add the shredded chicken and frozen peas and carrots. Mix everything gently.
Pour mixture into a greased baking dish and bake uncovered for 20 minutes until bubbly and golden on top.