Soak the green gram and brown rice in water for 5 hours. Drain the water. Start with grinding green chillies, curry leaves, coriander leaves, cumin seeds, spinach and coconut in a food processor. Grind them to a smooth paste. Remove and store in a fresh bowl where you plan to store the batter.
Now add the green gram, brown rice and little salt,g grind them to a coarse paste.
You could do it in two batched. For the first batch grind them to a smooth paste and set aside. Then for the second batch grind them to a coarse paste. The coarseness will make your dosa crisp up well.
Mix them all together with salt and store for 2 hours. If it is too thick, you could add little water to bring it to a pancake batter like consistency.