Heat oil in a pan. Add the cumin and the red dry chili or slit, fresh hot pepper and let them sizzle and turn slightly brown.
Add the onions and cook on medium heat till they start to caramelize. Add the potatoes, salt and the turmeric; stir them around the pan so all the spices and onions coat the potatoes.
Fry the potatoes for about 2 minutes, until the potato cubes start having a glazed look. Add garlic, mix well and cook until fragrant.
Add the grated/finely chopped tomatoes, stir to combine and cover and cook for about 2-3 minutes, at medium heat.
Add the spinach, toss everything together & cover the pan. Cook for about 5-8 minutes at medium heat or until the potatoes are cooked through and the spinach is wilted but still bright green.
Uncover the pan and increase the heat to high. Cook while tossing everything frequently until all the water evaporates and you hear a light sizzle. When some of the spinach starts to stick at the bottom of the pan, switch off the heat immediately. Cover the pan and let it sit for a couple of minutes.
Sprinkle fresh lime or lemon juice and serve immediately with hot steamed rice or flat bread and dal/lentils.