Boil pasta in heavily salted water 1–2 minutes longer than package directions, until very soft but not mushy. Drain, rinse with cold water, and transfer to a large mixing bowl.

While pasta is still slightly warm, toss with apple cider vinegar. Chill in the refrigerator for 10–15 minutes.

Add shredded carrots, 2 cups of mayonnaise, and drained tuna to the chilled pasta. Stir well to combine. Season with salt and pepper to taste. Refrigerate for at least 1 hour (overnight preferred).

Before serving, check the consistency. If dry, mix in the reserved ½ cup of mayo. Optional but highly recommended: add green peas for a touch of sweetness. Adjust seasoning as needed and serve cold.