In Multipurpose Steamer, add noodles and water. Cover; microwave on high until tender, 7–8 min.
Meanwhile, in a large bowl, whisk together mix, mayonnaise, and lemon juice. Set aside.
Dice peppers and celery. Place in bowl with dressing.
When pasta is cooked, drain and rinse with cold water. Drain tuna. Add pasta, tuna, and peas to bowl; stir to mix. Taste and season with pepper and fresh lemon juice, if desired.