Bring a large pot of salted water to a boil and cook pasta shells according to package directions until al dente.
Drain the pasta, reserving 1/4 cup of the pasta water, and set aside.
Pat the steak cubes dry with paper towels and season with salt, pepper, and Italian seasoning.
Heat olive oil in a large skillet over medium-high heat until shimmering.
Add the steak cubes in a single layer, searing for 2-3 minutes per side until browned and cooked to desired doneness.
Remove the steak from the skillet and set aside on a plate.
Reduce heat to medium and add butter to the same skillet, scraping up any browned bits from the bottom.
Add the minced garlic to the melted butter and sauté for 1 minute until fragrant.
Whisk in the reserved pasta water to the skillet to create a light emulsion.
Add the cooked pasta and steak bites back into the skillet, tossing thoroughly to coat in the garlic butter.
Remove from heat, sprinkle with Parmesan cheese and fresh parsley, and serve immediately.