Cut the base off the bok choy head and separate into individual stalks. Lay stalks out in a single layer on a baking sheet.
Mix the melted butter, miso, and gochujang together until completely combined. Brush mixture evenly over the surface of the bok choy stalks. Pro tip: some of the miso gochujang butter will inevitably drip off of the bok choy before it makes its way to the grill. Don’t let a bit of that tasty stuff go to waste - toss it with the grilled bok choy after it comes off the grill for extra deliciousness.
Transfer bok choy stalks on the hot side of the grill (perpendicular to the grill grates), and grill until stalks are tender and leaves are beginning to char, about 5-6 minutes, flipping once halfway through.
Return grilled bok choy back to the baking sheet, making sure to mix it with any of the butter mixture that dripped onto the pan before grilling. Serve bok choy in stalks, or chop into bite sized pieces.