Preheat the oven to 400°F.

Heat a 10-inch oven-safe skillet over medium heat. Add the olive oil and diced onion. Cook for about 3–4 minutes, stirring occasionally, until the onion begins to soften.

Sprinkle the flour over the onion and stir well. Cook for about 1 minute to remove the raw flour taste.

Gradually pour in the chicken broth, stirring constantly to prevent lumps.

Add the milk, thyme, garlic powder, salt, and pepper. Continue cooking for 3–5 minutes, stirring frequently, until the sauce thickens enough to coat the back of a spoon.

Stir in the cooked chicken and mixed vegetables.

If you're using frozen vegetables, there's no need to thaw them first. Allow the mixture to heat through for several minutes.

The filling should be creamy but still loose enough that it can bubble around the biscuit topping. If it seems too thick, add another splash of broth or milk.

In a small bowl, stir together the baking mix and milk until just combined.

Don't overmix. A few small lumps are perfectly fine.

If using them, gently stir in the Parmesan and dried parsley.

Drop the biscuit dough by spoonfuls over the chicken mixture, leaving a little space between the biscuits so steam can escape.

You don't need to completely cover the filling. In fact, leaving a few little windows of creamy chicken and vegetables showing makes the finished skillet look especially inviting.

Carefully transfer the skillet to the preheated oven.

Bake for 15–20 minutes, or until the biscuits are golden brown and cooked through and the filling is bubbling around the edges.

If the biscuits brown before they're completely cooked inside, loosely cover the skillet with foil and continue baking until done.

Let the skillet rest for about 5 minutes before serving.

That gives the filling a chance to settle while the biscuits finish soaking up a little of that creamy sauce.

Spoon directly from the skillet and enjoy.