Fill a large stock pot with water, add a generous pinch of salt, and bring to a rolling boil. Add rotini and cook until al dente according to package directions, usually 9-11 minutes. Reserve 1/4 cup of pasta water before draining.
Drain the pasta in a colander and rinse under cold running water for 30-60 seconds, tossing to ensure all pasta is cooled. Let it sit in the colander to drain fully, then transfer to a large mixing bowl.
In a small bowl, whisk together olive oil, lime juice, minced garlic, cumin, salt, and pepper until slightly thickened. Taste and adjust seasoning if needed.
Halve the cherry tomatoes, finely dice the red onion and jalapeño (if using), drain or thaw the corn, and chop the cilantro, setting a small amount aside for garnish.
Add the tomatoes, corn, red onion, and jalapeño to the cooled pasta. Pour the dressing over the top and toss with tongs until evenly coated. Add a splash of reserved pasta water if the mixture looks dry.
Just before serving, dice the avocados into bite-size cubes. Add the diced avocado and crumbled cotija cheese to the bowl. Fold gently with a spatula or tongs until just combined, being careful not to overmix.
Sprinkle the reserved chopped cilantro over the top. Serve right away, or within an hour, for the best texture.