How to Make It
In a food processor, combine the 11/2 cups of mint with the pistachios and lemon juice and pulse until finely chopped. With the machine on, gradually add the olive oil until incorporated and the pesto is nearly smooth. Scrape into a large bowl and season generously with salt and pepper.
Meanwhile, in a large saucepan of salted boiling water, cook the pasta until al dente. Drain well, reserving 1 cup of the cooking water. Add the pasta, chicken, zucchini, yellow squash, tomatoes and reserved cooking water to the pesto and toss well. Season generously with salt and pepper and toss again. Garnish with mint leaves and serve right away.