Pour oil and mustard seeds into a large frying pan. Cook over medium-high heat, covered, until seeds finish popping, about 1 minute. Add garlic and chile and cook, stirring, until garlic just starts to brown, about 1 minute.
Add squash and stir to coat. Add 1/2 cup water, cover, and cook until squash is tender to the bite, 20 to 25 minutes. Sprinkle with salt to taste and garnish with cilantro if you like.
Note: Nutritional analysis is per serving.