Grease a baking tin with some butter and dust with some flour.
Take yeast in a bowl. Add ½ teaspoon castor sugar and 2-3 tablespoons warm water, mix and set aside to activate.
Take semolina, salt and 1½ cups water in a bowl and mix. Add activated yeast and knead.
Add 2 tablespoons oil and knead well. Transfer the dough on the worktop and knead well to make soft dough. Transfer into the same bowl, cover with cling film and set aside to prove for 15-20 minutes.
Heat remaining oil in a non-stick pan. Add mustard seeds and let it splutter. Add green chillies, curry leaves and onion and sauté till onion turns golden.
Add tomato and sauté for 1 minute. Add salt, mix and cook for 1 minute. Transfer into another bowl and cool.
Add it to the proved dough and knead well. Transfer the dough into the greased tin and level it out. Cover with cling film and set aside to prove for 15-20 minutes.
Preheat oven to 180º C.
Place the tin on a baking tray. Place the baking tray in the preheated oven and bake for 15-20 minutes, basting with some butter a couple of times. Remove from oven, cool and demould.
Slice and serve.