Bring a large pot of salted water to a boil. Cook the penne or rotini according to package instructions until al dente. Drain and set aside.
Heat 1 tablespoon of olive oil in a cast iron skillet over medium-high heat. Season the bite-sized steak pieces with salt, pepper, garlic powder, and onion powder. Add the steak to the hot skillet and sear until browned on all sides but still tender inside, about 3-4 minutes. Remove the steak and set aside.
In the same skillet, add the remaining tablespoon of olive oil. Add the thinly sliced onions and cook on medium heat, stirring often, until they turn golden brown and crispy, about 10-12 minutes. Remove half of the onions for topping later.
To the skillet with the remaining onions, pour in the heavy cream and beef broth. Stir well, scraping any browned bits off the bottom of the pan. Let the sauce simmer gently until it thickens slightly, about 5 minutes. Stir in the shredded cheddar cheese until melted and smooth.
In a large mixing bowl, combine the cooked pasta, seared steak pieces, chopped spinach, crumbled turkey bacon, and creamy cheddar sauce with onions. Toss everything gently to coat the pasta evenly.
Preheat your oven to 375°F (190°C). Transfer the pasta mixture into a greased 9x13 baking dish. Sprinkle the reserved crispy onions evenly over the top for an irresistible crunch. Bake uncovered for 20-25 minutes, until the top is golden and bubbly.
Remove from the oven and let it rest for a few minutes before serving. This dish pairs beautifully with a fresh green salad or roasted vegetables for a complete meal.