Preheat grill. Spread butter on both sides of steak. Sprinkle salt and pepper on both sides of steak.
Grill 3-4 minutes per side, or to desired doneness. Remove from grill and let stand 5 minutes.
While steak is standing, arrange spinach evenly among 5 salad plates, bowls, or prep containers. Top evenly with halved tomatoes, crumbled feta, and peeled and halved hard boiled eggs. Cube steak and add to salad.
Balsamic Vinaigrette
Add all ingredients to a shaker cup or blender. Shake or blend to combine. Arrange vinaigrette evenly over salad, or, if prepping ahead, into water-tight containers.
Notes
We used the Instant Pot to cook the eggs (RECIPE HERE).For dairy free, omit feta.For vegetarian, omit steak.For vegan, omit steak, eggs, and feta and replace with pecan halves.