In a pan, heat 1 tsp of a neutral-tasting oil. 

Add the mustard seeds to the pan and wait till they pop.

Once they pop, add the cumin seeds, green chilies, ginger, and garlic paste. Saute on low-medium heat for 2-3 minutes.

Stir in the onions and sauté until translucent.

Add turmeric, coriander, and red chili powder. Sauté, stirring continuously to prevent burning, for 2-3 minutes.

Stir in the tomatoes, salt, and a ¼ cup of water. Cook for 5-6 minutes until tomatoes turn mushy and are well combined with the onions.

Add cubed potatoes and another ¼ cup of water (if desired). Cover and cook for 10 minutes or until the potatoes are fork-tender. 

Stir in the green peas. Cover and cook for another 5 minutes or until the peas are cooked through. 

Gently mash some of the potatoes with the back of a spatula or a potato masher. This will thicken the consistency of the sauce. 

Let the sauce cook down until it thickens to your desired consistency.

Garnish with freshly chopped cilantro and serve with pooris, naan, or roti.