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.
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.
Cover with foil and bake for 25-30 minutes. Remove foil and bake another 5 minutes, until cheese on top is melted, if needed.