Shrimp ‘n’ Shells Salad

8 ounces uncooked small pasta shells
1 cup fat-free mayonnaise
1/4 cup grated Parmesan cheese
1/4 cup 1% buttermilk
1/3 cup finely chopped onion
2 tablespoons minced fresh parsley
1 1/2 teaspoons minced fresh basil
1/2 teaspoon salt
1/2 teaspoon pepper
1 pound cooked medium shrimp, peeled and deveined
1/4 cup frozen peas, thawed
1/4 cup diced pimientos
1 medium tomato, seeded and chopped
2 green onions, thinly sliced

Cook pasta according to package directions. Meanwhile, for dressing, combine the mayonnaise, Parmesan cheese, buttermilk, onion, parsley, basil, salt and pepper in a blender or food processor; cover and process until blended

Drain pasta and rinse with cold water. In a large bowl, combine the pasta, shrimp, peas, pimientos, tomato and green onions. Add dressing and toss to coat. Cover and refrigerate until chilled.