Cook macaroni to al dente following directions on the package. Drain and rinse in a colander and drain well. Cool to at least room temperature, or in the fridge.
Meanwhile, in a large bowl combine tuna, celery, onion, eggs and peas. Seasoning with a little salt and pepper. Stir in cooked macaroni.
In a small bowl, stir together mustard, mayonnaise and pickle relish. Pour dressing over the macaroni mixture and stir to coat completely. Taste and add salt and pepper as desired.
Store in a tightly sealed container for up to 3-5 days. If salad seems dry, add a couple of tablespoons of mayonnaise to moisten.
Nutritional values are approximate and are based on 10 servings per batch, served as a light meal or hearty side dish.Feel free to adjust the ingredients as you like, adding more or less of each. How to Prep Ahead: You can this salad up to a day in advance; in fact it's recommended to make it at least a few hours ahead. Tighty cover and store in the refrigerator. Just before serving, you can add a little more mayo if it seems dry.Storage: For leftovers, store in an airtight container in the fridge for up to 3-5 days. If needed, add a little more mayo to moisten when serving. Do not freeze.