Preheat oven to 375°F. Heat oil in 10-inch oven-safe skillet over medium heat. Add onion and sauté until soft and translucent, about 5 minutes. Add garlic and sauté for another 2-3 minutes. Sprinkle with flour and stir to coat onion mixture. Pour in both cans of cream of chicken soup, frozen vegetables, and dried thyme (optional), and stir to combine well. Reduce to heat to low and cook until heated through and just bubbling, 5 to 10 minutes. Stir in chunk chicken and remove skillet from heat. Separate biscuits and place gently on top of chicken and vegetable mixture. Brush with 2 tablespoons melted butter. Bake in preheated oven until golden brown, about 16-20 minutes. Remove from oven and let stand for 5 minutes before serving.