Peel the ridge gourd and chop into small, even ½-inch pieces. Chop brinjal the same size. Finely dice the onion. Soak toor dal in water while you prep 15 minutes is enough.
Add peerkangai, kathirikai, soaked toor dal, onion, red chillies, turmeric, tamarind water, salt and 1 cup of water into the pressure cooker. Stir gently to combine. Do not mash at this stage.
Pressure cook for 4 whistles . Close the lid and heat on high until the first whistle. Reduce to medium-high heat and cook for 3 more whistles (about 10–12 minutes total). Turn off the heat immediately after the 4th whistle. Let the pressure release
Open the cooker once pressure has fully released. Use a ladle to mash everything together until creamy with some small chunks still visible. This is the classic kadayal texture — do not over-mash into a paste
Heat 1 tbsp gingelly oil in a small pan on high heat. Add mustard seeds and wait for them to splutter. Add cumin seeds and fresh curry leaves — the leaves will darken in about 15 seconds. Pour the hot sizzling tempering directly over the masiyal and mix immediately. Serve warm.