There is another way of preparing Kerala style kanji payar using rice and cherupayar (mung beans) by cooking them together in the same pressure cooker and this is a different style of preparation which is more easy to do as well. When I post the recipe for one pot kanji payar recipe in my blog, I will link to the recipe from here.
The Kerala style seasoning using coconut oil, mustard seeds and red chilies is not a must, but adding it will make the dish more delicious. You may also prepare the seasoning in the same pressure cooker where you prepared the cherupayar thoran, by making it in the beginning before you add the green mung beans to the cooker and thus make it even more easier.
As I mentioned, you can also serve the kanji or Kerala style rice soup with thoran made of other varieties of legumes like red cowpeas, horsegrams etc though the green mung beans (cherupayar) thoran is the most popular and traditional combination.