Pre-cook the potatoes in boiling salted water. Set aside.
Coarsely chop the spinach.
Heat a saucepan large enough to hold all the ingredients over medium low heat.
Add the oil. When it starts to shimmer, add the cumin and mustard seed and cook until they start to barely crackle.
Add the oil and onions and cook, stirring occasionally, until the onions are soft.
Mix in the garlic ginger paste and cook another minute or so.
Stir in the red chili, indian restaurant spice mix (or curry powder), turmeric and salt. Cook, stirring constantly, for about 30 to 45 seconds. Be careful not to burn the spices.
Add the water or curry base and cook about 30 seconds. Mix in the chopped spinach and potatoes and cover. Cook until the the spinach is wilted and potatoes are hot.