Preheat oven to 350°F and coat a 9-by-13-inch casserole dish with nonstick spray.
Bring a large pot of salted water to a boil. Cook penne just to al dente, according to package directions. Reserve 1/2 cup pasta water, drain and return to the pot or transfer to a bowl. Toss with olive oil and set aside.
16 ounces penne pasta, 1 tablespoon olive oil
In another bowl, stir together ricotta, pesto, and cream until blended. Add reserved pasta water, a little at a time, to thin if desired. Pour sauce over pasta and stir well to coat. Stir in the chicken and tomatoes, then transfer to prepared dish. Sprinkle on shredded mozzarella.
1 cup ricotta, 1/3 cup pesto, 2 tablespoons heavy cream, 2 cups diced cooked chicken, ¼ cup chopped oil-packed sun-dried tomatoes, ½ cup shredded mozzarella
Cover with foil and bake for 25-30 minutes. Remove foil and bake another 5 minutes, until cheese on top is melted, if needed.