Cook ziti until almost done, drain and set aside in a large mixing bowl.
Preheat the oven to 350° and lightly grease a casserole dish.
Make sure to freeze your steak for about half an hour before cutting. (Freezing it will help with cutting it thinly.)
Slice partially frozen steak as thin as possible. Slice red pepper, mushrooms, and onion thinly as well and set aside.
Preheat some oil (about a tablespoon or two) in a medium sauté pan, over medium heat and sauté steak, peppers, mushrooms, and onions with some salt and pepper until steak is no longer pink.
Add steak and veggies to the bowl with pasta. Add a 1 ½ cup of Mozzarella, Ragú® sauce, thyme and some more salt and pepper. Mix well and place it into a lightly greased casserole dish. Spread evenly and top off with remaining Mozzarella cheese.