Pesto Pasta with Peas & Tomatoes

•  8 ounces whole-wheat rotini (about 2 cups)
• 1 cup frozen peas
• ¼ cup pesto
• 2 tablespoons reduced-fat mayonnaise
• 1½ tablespoons white-wine vinegar
• ¼ teaspoon salt
• ¼ teaspoon ground pepper
• 1 cup quartered grape tomatoes
• 1 scallion, sliced (about ¼ cup)

1. Bring a large saucepan of water to a boil. 
2. Add 8 ounces pasta; cook for 3 minutes less than package instructions.
3.  Add 1 cup peas and continue cooking until the pasta and peas are tender, about 3 minutes more. 
4. Drain the pasta and peas.
5. Meanwhile, whisk ¼ cup pesto, 2 tablespoons mayonnaise, 1½ tablespoons vinegar, ¼ teaspoon salt and ¼ teaspoon pepper together in a large bowl.
6.  Add 1 cup tomatoes, the sliced scallion and the cooked pasta and peas. 
7. Stir until well combined. Serve warm or at room temperature.