Preheat the oven to 375°F. Lightly grease a 9×13-inch baking dish to keep the casserole from sticking.
Bring a large pot of salted water to a boil. Prepare the shell pasta according to the package instructions until it reaches an al dente texture. Drain thoroughly and set aside.
While the pasta cooks, place a skillet over medium heat. Add the ground beef and cook, breaking it into crumbles, until completely browned with no pink remaining. Season to taste with kosher salt and freshly ground black pepper. Seasoned salt or garlic powder may also be used if desired.
Transfer the drained pasta and cooked ground beef to the prepared baking dish. Add the condensed tomato soup, ½ cup water, and half of both the cheddar and mozzarella cheeses. Stir thoroughly so the beef and pasta are evenly covered with the tomato mixture and cheese.
Scatter the remaining cheddar and mozzarella evenly over the casserole. Cover the baking dish with foil and bake at 375°F for 20 minutes.
Remove the foil and return the casserole to the oven for another 10 minutes. For a lightly crisp and browned cheese surface, broil for an additional 2–3 minutes, monitoring closely to prevent scorching.
Serve the casserole hot.