Place the tempeh into a steamer basket and set over a pot filled with 1-inch of water. Bring the water to a simmer, cover, and let steam for 10 minutes. Remove, let cool, and use your hands to crumble the tempeh.

Heat the oil in a medium skillet over medium heat. Add the mushrooms and cook until soft, about 5 minutes. Add the tempeh and tamari and cook for 2 to 3 more minutes. Transfer to a bowl and add the scallions, kimchi, sesame oil, ginger, and sriracha. Stir to combine.

Assemble the dumplings by scooping 1 heaping teaspoon of the filling onto each wrapper. Using your fingers, dab the edges of the wrapper with cold water, fold in half over the filling, and press to seal. Fold 3 pleats into the wrapper at the top of the crescent.

Place the dumplings in the bamboo steamer without touching each other and cover with the lid. Bring 1 inch of water to a simmer in a skillet that the steamer can hover over. Place the steamer on top and steam for 10 minutes. Serve with tamari or chili oil for dipping.