Bring a large pot of lightly salted water to a boil; add penne and cook, stirring occasionally, until tender yet firm to the bite, about 11 minutes. Drain.
Melt butter in a large saucepan over medium-high heat. Add minced garlic; saute until golden, about 30 seconds. Stir in cream cheese until smooth. Add milk; stir until there are no lumps. Lower heat to medium. Add 3/4 of the Parmesan cheese, parsley, Italian seasoning, 1/2 teaspoon salt, and black pepper. Simmer, stirring occasionally, until sauce is smooth, about 5 minutes. Remove from heat.
Heat olive oil in a large skillet over low heat. Season chicken with 1/2 teaspoon salt and garlic powder on both sides. Cook chicken breasts until no longer pink in the center and an instant-read thermometer inserted into the center reads at least 165 degrees F (74 degrees C), about 6 minutes per side. Cut chicken into 1/2-inch cubes.
Preheat oven to 375 degrees F (190 degrees C).
Butter bottom and sides of a 9x13-inch casserole dish. Cover bottom with a layer of pasta. Place half of the chicken cubes on top. Pour 1/2 of the sauce over the chicken. Repeat layering pasta, chicken, and sauce. Sprinkle top with remaining Parmesan cheese. Cover with aluminum foil.
Bake in the preheated oven until sauce is bubbly, about 15 minutes. Remove aluminum foil and bake until cheese is golden, about 5 minutes more.