Wash and rinse all the grains two to three times till the water runs clear.
Now soak the rice and quinoa together and urad dal separately for at least 3-4 hours. For no-rice method, you can just wash poha and soak it with either urad dal or quinoa.
I prefer to soak them for 8 hours for the best results.
After the soaking, grind all the grains with soaked fenugreek until smooth. I prefer to use a high-speed blender for this process. You can always use a wet grinder as well.
I prefer to keep the rice and quinoa batter little grainy and the urad batter fully smooth. The grainy rice texture adds a nice texture to the idlies. But it's totally optional. If you want to keep the rice batter grainy, make sure there are no big pieces of grains left. The batter should feel grainy when you rub between your fingers but should look smooth. For the no-rice version, grind everything to a smooth batter.
Mix all the batters well. Add salt at this point, and mix really well.