Grate the lauki using the middle hole of a box grater. Measure out 1 cup of grated lauki. Add the grated lauki to a pressure cooker along with ½ cup water and stir well.
Pressure cook for 2 whistles on high heat.
Remove the cooker from heat and let the pressure release naturally.
Strain the lauki using a fine-mesh strainer and let it cool completely.
Whisk yogurt in a medium size mixing bowl using a wire whisk until smooth and creamy.
Add cooked lauki, green chilies, cilantro, black salt, and roasted cumin powder to the bowl and mix well.
Chill the raita for a few hours and serve.