Steam or boil the diced potatoes until just tender, about 10 to 12 minutes. Drain and set aside.
Heat the oil over medium-high heat in large sauté pan, or medium size, non-reactive Dutch oven. After 90 seconds when the oil is hot, add the mustard seeds and cumin seeds, allowing them to sizzle and pop for a few seconds until fragrant.
Add the cauliflower florets and diced onion. Stir well and cook for five to seven minutes until the onions are softened and the cauliflower begins to tenderize and become lightly golden all around.
Reduce the heat to medium and stir in the minced garlic, grated ginger, green chilies, garam masala, dried kasuri methi (if using), turmeric, amchur, and Kashmiri red chili powder. Cook for 2-3 minutes, allowing the spices to bloom and coat the vegetables.
Add the chopped cilantro, tomato puree, cooked potatoes and salt to the pan, stirring to combine. Cook over medium-low heat for another 4-6 minutes until the cauliflower is fully tender.
Transfer the aloo gobi into an attractive serving dish, or portion into bowls over rice. Garnish with fresh cilantro leaves, strips of green chili, and finely minced red onion if desired. Serve hot.