Preheat the oven to 350°F (175°C). Spray a 9x13-inch baking dish with cooking spray and set aside.
Cook the penne pasta according to package directions until al dente, then drain in a colander and set aside.
In a medium saucepan over medium heat, combine the heavy whipping cream and cream cheese, stirring until the cream cheese is fully melted and the mixture is smooth.
Whisk the grated Parmesan cheese and the Fiesta Ranch seasoning packet into the cream mixture until evenly incorporated and smooth.
In a large mixing bowl, toss the cooked pasta with the cream sauce until well coated. Add the cubed cooked chicken and drained black beans, and mix to combine.
Transfer the pasta mixture to the prepared baking dish, spread evenly, and sprinkle the shredded mozzarella over the top.
Bake for 20–25 minutes, until the casserole is heated through and the cheese is bubbly. Remove from oven.
Top with sliced green onions and diced tomatoes, then serve warm.
