In a large skillet heat oil over medium high heat, add all filling ingredients excluding tofu, bak choy and corianders. Cook mixture until fragrant and mushrooms cooked off. Add tofu, bak choy, and stir-fry for another 2-3 minutes. Transfer mixture to a large mixing bowl and allow to cool. Then add the corianders and mix well.
In a stand mixer, add flour, salt and water, knead (using a dough hook) until you have a smooth dough. Remove half of the dough from the mixer, set aside. Add red beet powder into the half dough and continue kneading until combined. Let doughs rest for 20 minutes.
Roll white and red dough into 2 rectangle pieces (same length) Cut strips of both red and white, white about 1 inch wide and red 1/2 inch. Line up strips (see picture)
Gently roll again with your rolling pin to seal layers. Cut a circle using a cookie cutter. Then flatten each piece into a thin wrapper with a rolling pin.
Arrange 4 wrappers in a line, slightly overlapping each other. Spread filling onto the center of the wrappers. Fold in half and wet edges slightly with water. Starting at the end, roll it up tightly. Make sure the dumpling's properly sealed later on.
Repeat this step with all the wrappers and filling.