Heat the oil in a large heavy-bottomed pan over medium heat until shimmering. Add the cumin seeds and cook for about 30 seconds until they crackle and release a warm aroma.
Add the chopped onion to the pan and sauté, stirring occasionally, until it turns golden and soft, about 7-8 minutes. The kitchen will fill with a sweet, caramelized smell.
Stir in the minced garlic and grated ginger, cooking for another minute until fragrant and slightly bubbling.
Add the turmeric, cumin powder, and garam masala to the pan, stirring constantly for about 30 seconds to toast the spices and release their warm, smoky scent.
Introduce the diced potatoes to the pan, stirring well to coat them in the spice mixture. Cook for about 5 minutes, allowing them to start softening and develop a slight golden edge.
Add the drained chickpeas, stirring to combine everything evenly. Let cook for 2 minutes, allowing the flavors to meld.
Pour in the diced tomatoes, stirring to incorporate. Lower the heat to medium-low and simmer uncovered for about 15 minutes, until the sauce thickens slightly and the potatoes are tender enough to break apart gently when pressed.
Stir in the coconut milk, mixing thoroughly to create a rich, creamy sauce. Continue simmering for another 10 minutes, letting the flavors deepen and the curry thicken to a luscious consistency.
Turn off the heat and squeeze in the lemon juice. Taste and season with salt as needed. Let the curry sit covered for 5 minutes to allow flavors to meld beautifully.
Give the curry a gentle stir, then serve hot, garnished with fresh herbs if desired. The dish should be thick, with soft, broken-down potatoes and chickpeas swimming in a fragrant, vibrant sauce.
