Bring a large pot of water to boil. Once boiling salt the water, then add the macaroni. Cook until al dente. Drain and rinse in a colander under cold water. Transfer the noodles to a large bowl.
Add the tuna, carrots, onion, peas, cucumber, peppers, to the large bowl. Toss to combine. Place in the refrigerator (covered) while you make the dressing.
In a small bowl whisk the mayo, cider vinegar, sugar, and mustard. Pour the dressing over the pasta then stir to combine. Add the diced avocados right before serving (so they don’t turn brown). Top with chopped chives and freshly cracked pepper.
You can assemble beforehand. Keep chilled in the fridge… but don’t add the avocados until right before serving (as noted).