Brush a little oil on the base of your steamer basket or dish. Set up your steamer arrangement by filling it with water and keep it ready to go.
In a large bowl, add all the ingredients listed under "Muthiya" except water. Gently start squishing everything to combine. The lauki and spinach will start releasing their juices and you would be able to almost bring the dough together. If needed, add a tablespon of water at a time to form a firm yet soft dough. You can use yogurt in place of water as well. Dont knead the dough too much. Once a ball is formed, dough is ready.
Cover the dough with a cloth and rest it for 10 minutes. Meanwhile start your steamer so that the water is boiling when you are ready to steam.
Divide the rested dough into two portions. Shape the dough into thick logs.
Place the logs in the steamer. Make sure that the water is boiling when you place the logs. Steam for 18-20 minutes until a skewer when inserted in the middle comes out clean.
Switch off the stove and let sit covered to continue cooking in residual steam. After about 10-12 minutes when the logs are cool to touch, using a sharp knife, slice the logs into small portions. Use knife in a saw manner so as to not squish when you slice.
In a wide pan, add the oil for tempering. Crackle dried chilli, mustard and sesame seeds. Add the curry leaves, they will splutter. Place the sliced muthiya in a single layer in the tempering. Let pan fry for 3 minutes. Flip and repeat on the other side.
Once the muthiya are pan fried lightly, switch off the stove. Sprinke sugar, lemon juice and chopped cilantro. Add the grated coconut if using.Serve immendiately!