1 small (3 lb.) spaghetti squash 1 TBSP vegetable oil
1 tsp brown mustard seeds 3 TBSP unsalted butter
1/2 cup finely chopped yellow onion 2 tsp minced fresh ginger
2 tsp chopped garlic 1 tsp cumin seeds
1/2 tsp ground coriander 1/2 cup seeded and chopped tomato
1 small serrano chile, seeded and minced Kosher salt
1/2 cup coarsely chopped cilantro
Position a rack in the center of the oven and heat the oven to 400°F. Halve the squash lengthwise and scoop out the seeds with a sturdy spoon. Set the squash halves cut side down in a casserole dish with 1 inch of water. Cover and bake until a fork easily pierces the skin side of the squash, 20 to 35 minutes. Set the squash halves aside until cool enough to handle. Use a fork to rake the cooked squash flesh into strands.
In a 10-inch skillet, heat the oil over medium-high heat until hot. Add the mustard seeds and cover. The seeds will start popping; cook until the popping subsides, about 1 minute. Uncover, reduce the heat to medium, and add the butter. As soon as it melts, add the onion, ginger, garlic, cumin seeds, and coriander and cook, stirring, until the onion is soft, about 3 minutes. Add the tomato, chile, and 1 tsp. salt and cook, stirring, until the tomato begins to soften and the chile is fragrant, about 2 minutes.
Increase the heat to medium high and add the squash to the skillet. Continue to cook, tossing with tongs, until heated through, 1 to 3 minutes. Toss in the cilantro, season to taste with more salt, and serve.