Melt butter in a large skillet over medium high heat.
Using paper towels, pat both sides of the steak dry. Drizzle with olive oil; season with salt and pepper, to taste.
Add steak to the skillet and cook, flipping once, until cooked through to desired doneness, about 3-4 minutes per side for medium-rare. Let cool before dicing into bite-size pieces.
Place eggs in a large saucepan and cover with cold water by 1 inch. Bring to a boil and cook for 1 minute. Cover eggs with a tight-fitting lid and remove from heat; set aside for 8-10 minutes. Drain well and let cool before peeling and dicing.
To assemble the salad, place spinach into meal prep containers; top with arranged rows of steak, eggs, tomatoes, pecans and feta.