According to Sai Viswanath, this classic southern Indian dishspicy with chile peppers and aromatic with ginger and mustard seedsis too good to mess with: "I've eaten it forever and the flavor memory is so persistent, I just can't change it."
In a large saucepan of boiling salted water, cook the beans until crisp-tender, about 2 minutes. Drain, let cool and pat dry with paper towels.
In a large skillet, heat 2 tablespoons of the oil until shimmering. Add half of the mustard seeds and when they pop, add half each of the jalapeño, ginger and curry leaves and cook over high heat until fragrant, about 30 seconds. Add half of the green beans and toss until hot, about 30 seconds. Season with salt and transfer to a platter. Repeat with the remaining oil, mustard seeds, jalapeño, ginger, curry leaves and beans. Serve hot or at room temperature.