In a small bowl combine the Italian seasoning, garlic powder, salt, and pepper. Season the steak on all sides with the mixture and set aside.

Bring a pot of water to a boil and cook the pasta according to package directions. Reserve one tablespoon of the starchy water before draining the pasta.

While the pasta cooks heat one tablespoon of olive oil in a medium-sized pan over medium heat. Cook the steak for 5-7 minutes on each side (depends on how pink you like it - 7 minutes will be barely pink). Remove the steak from the pan and leave it on a plate to rest.

In a large bowl, whisk together 1/4 cup of olive oil,  the balsamic vinegar, and mustard until it's thickened.

Thinly slice the steak, against the grain and place it in the bowl with the dressing along with the pasta, reserved pasta water, spinach, and parsley. Toss it all together. As you toss it the spinach will wilt.

Garnish with the feta cheese and serve the pasta warm, at room temperature or you can chill it before serving. If you chill it, hold off adding the cheese until serving and give the pasta and steak a toss before serving.