Bring large saucepan of lightly salted water to a boil. Add potatoes, return to a boil, and cook until fork-tender, 7 minutes; remove with slotted spoon and set aside, reserving the cooking liquid.
Add lentils to the same saucepan and return cooking liquid to a boil. Cook until lentils are tender but still hold their shape, 8 - 10 minutes; drain and set aside.
Heat a large nonstick skillet over medium-high heat. Swirl in the oil, then add the onion, jelapeno, garam masala, and cumin. Cook until onion begins to soften, 3 - 4 minutes. Stir in the potatoes, tomatoes, chickpeas, ginger, and garlic. Cook, stirring occasionally, until tomatoes soften and potatoes are tender, 4 - 5 minutes. Stir in lentils and cook until heated through, 1 minute. Remove from the heat and stir in cilantro.