Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C).

Bring a large pot of lightly salted water to a boil; cook rotini at a boil until tender yet firm to the bite, about 8 minutes; drain.

Meanwhile, melt butter in a large skillet over medium heat; cook and stir onions until translucent, 8 to 10 minutes.

Transfer onions to a large bowl and mix in pasta, tomato soup, hot dogs, corn with juice, dill pickle relish, and yellow mustard.

Pour mixture into a baking dish.

Bake in the preheated oven until bubbling and top is lightly browned, about 1 hour.