Pressure cook the toor dal, onion, tomatoes, green chilli, zucchini, ginger, garlic and a cup of water for 3 whistles. (Adjust the dal as required, but zucchini contains sufficient water so do not add too much water. Your dal will turn too watery).
Coarsely grind peppercorns and cumin seeds and keep aside.
Blend the pressure cooked vegetables with a hand blender. Add salt.
Heat oil in a pan, splutter the mustard seed, urad dal, asafoetida powder, curry leaves and red chillies.
Mix them with the blended zucchini dal.
Add ground peppercorns and cumin seed powder. Adjust the taste as required. If you want it spicier add more of the ground powder.