Preheat the oven to 425° F. Lightly grease a baking dish or use an oven-safe skillet and skip the dish. Bring a large pot of salted water to a boil over high heat and boil the pasta until al dente according to package directions. Reserve 1 cup of pasta cooking water, then drain. Meanwhile, cook the chicken sausage and zucchini in a large skillet over medium heat until browned all over, about 5 to 8 minutes. Reduce the heat to low, add the tomato paste, thyme, and oregano. Cook 1-2 minutes, then add the vodka. Simmer 1 minute, pour in the milk plus 1/3 cup pasta cooking water. season with salt and pepper. Simmer for 10 minutes or until the sauce thickens slightly, but is still saucy. Taste and adjust seasonings as needed.In a medium bowl, combine the ricotta, provolone, and 1/2 cup pesto. To assemble, spoon 3/4 of the sauce into the bottom of the prepared baking dish. Working with one pasta shell at a time, spoon about 1 tablespoon of the cheese mixture into each shell, placing the filled shell into the baking dish as you go. Spoon the remaining sauce over the shells, then drizzle the remaining pesto. Add the mozzarella.Bake 15-20 minutes or until the cheese has melted. Serve with fresh basil. Enjoy!