Grind coconut and jeera to a fine paste by adding little water to it. Set aside.
In a kadhai or saucepan add pumpkin, turmeric powder, chilli powder, salt, water and cook until it gets well cooked.
Once the pumpking gets well cooked, mash it well.
Now add the coconut paste to the mashed pumpkin, mix well and cook on low flame for 5-7 mins.
In the meanwhile in another pan, add oil and crackle mustard.
Once the seeds starts crackling add curry leaves and whole red chilli.
Now add coconut to it and fry the coconut until golden brown. (keep stiring, the coconut should not get burnt)
Add the fried coconut mixture to the pumpkin curry and mix everythng well. (Do not cook after adding the fried coconut, just keep it covered for some time)
So the mathanga erissery is ready now, you can serve it along with plain rice.
People from south India prefers to have it along with boiled rice, but you can also have it along with white rice as well.
You can make any side dish of your choice if you want.
Normally I prefer to have this curry along with rice and papdam or papad, without and side dish.