Start by boiling a large pot of water. Add the elbow macaroni and cook until tender but still firm, about 7-9 minutes. Keep an eye on it to avoid overcooking, as it can turn mushy.
Once the pasta is ready, drain it and rinse it under cold water immediately. This stops the cooking and helps separate the pasta to prevent it from sticking together.
In a large mixing bowl, whisk together the mayonnaise, apple cider vinegar, granulated sugar, and dijon mustard until creamy and well-combined. Taste the dressing; adjust the vinegar to your liking as too much can overpower the flavors.
Gently toss in the drained tuna, shredded carrots, diced red onion, diced red bell pepper, and diced green bell pepper. Stir carefully to avoid breaking up the tuna too much, maintaining some chunky bites.
Just before serving, add the diced avocados to the salad. This step keeps the avocados fresh and prevents browning. If you have chilled the salad, this is the final touch to maintain the avocado's firmness.
Sprinkle salt and ground black pepper into the salad and stir well. Adjust seasoning according to your preference, being generous with the pepper for a bit of extra kick, but cautious with the salt.
If time allows, let the salad chill in the fridge for 15-20 minutes to allow the flavors to meld, but remember to add the avocado right before serving to keep it vibrant.