Heat oven to 400°F. Grease a 9x13-inch baking dish.
Warm olive oil and butter in a skillet over medium heat.
Cook onion until soft, about 3 minutes. Stir in garlic for 30 seconds.
Sprinkle in flour. Stir and cook one minute to remove raw taste.
Whisk in broth, soup, and milk until smooth and steamy.
Fold in mixed vegetables and chicken. Season with salt, pepper, and thyme.
Simmer 2 to 3 minutes to slightly thicken. Remove from heat.
Spread filling in the baking dish. Sprinkle cheese if using.
Cut biscuits into halves or quarters. Arrange evenly over the filling.
Bake 22 to 26 minutes, until biscuits are deep golden and bubbly.
Rest 5 minutes. Garnish with parsley and serve warm.
Notes
Variation: Add 1/2 tsp poultry seasoning or swap cheddar for pepper jack. For a pot pie vibe, use smaller biscuit pieces. Leftovers keep 3 days refrigerated; reheat covered at 350°F until hot.This recipe is an original creation inspired by classic Easy Chicken and Biscuits Casserole flavors. All ingredient ratios and instructions are independently developed.