Put half the turmeric and chilli powder in a small bowl, add 2 tablespoons of water and mix together.
Cut the paneer into 5-cm / 2-inch cubes and with a sharp knife, score them all over lightly. Put them in a large, shallow dish and pour over the turmeric mixture. Season and set aside for about 10 minutes.
Heat 1 tablespoon of oil in a heavy-based pan over medium heat, add all the spice seeds at once, and stir-fry for 1 minute, or until they start to splutter.
Add the onions and chillies and cook for about 5 minutes, or until the onions turn light brown. Add the ginger and garlic pastes and the remaining turmeric and stir-fry for about 1 minute.
Stir in the yoghurt, then while stirring, sprinkle over the amchoor and garam masala and season with salt.
Reduce the heat to low and cook for about 2 minutes, or until the moisture has reduced a little, but make sure that the liquid does not dry up completely.
Add the marinated paneer and peppers and cook for a further 3 minutes, then remove from the heat and allow to cool.
Heat just before serving and garnish with slit green chillies.