Put the optional tofu and optional tamari in a medium bowl and toss gently. Set aside.

Quarter the mushrooms lengthwise. If the bok choy clusters are very small, they may be left whole or quartered lengthwise; otherwise,cut them crosswise into slices about ½-inch wide.

Put a large saucepan over high heat and add the oil. Tilt the saucepan back and forth until the oil melts and is evenly distributed. Add the mushrooms and bok choy. Stir briskly to prevent sticking until the bok choy wilts, about 1 minute.

Stir in the curry paste until well distributed. Add the coconut milk and stir until well combined. Bring to a boil, decrease the heat to medium, and simmer until the mushrooms are tender, about 4 minutes.

Add the tofu, if using, and warm through, about 5 minutes. Remove from the heat and stir in the cilantro. Divide among four bowls and garnish generously with the scallions. Serve at once.