Melt ghee in a dutch oven or heavy-bottomed pot over medium heat, add cumin seeds and once they start to splutter, add the serrano pepper, and stir-fry for 30 seconds. Then add the water, onion masala, peas, spices and mix well.
Bring the mixture to a boil, then reduce the heat to medium, add the paneer and cover with a lid. Cook for 1-2 minutes (if using frozen onion masala, just make sure it has melted into the sauce).
Remove the lid, stir, add the cream and cook for another minute.
Garnish with cilantro and serve.