Place eggs in a saucepan and cover by 1 inch with water. Place on a burner over high heat and bring to a boil.
Remove the pan from the stove, cover, and let sit for 10 minutes. Run cold water over the eggs, then peel and chop.
Meanwhile, bring a large saucepan of water to a boil. Cook pasta according to package directions.
Add the snap peas to the pasta for the last minute of cooking time. Drain the peas and pasta, and rinse with cold water.
While the pasta is cooking, whisk together the buttermilk, mayonnaise, most of the dill (reserve a little dill for garnish), vinegar, salt, and pepper in a large bowl.
Stir in the pasta, snap peas, celery, radishes, pickles, and onion.
Gently stir in the tuna, taking care not to break it up too much.
Transfer the pasta salad to a large serving bowl, and top with the chopped eggs and remaining dill. Serve immediately, or refrigerate the salad until ready to serve.