Season the ribeye steak with olive oil, salt, and black pepper.
Let it sit for about 5 minutes to absorb the flavors.
Preheat a skillet over high heat.
Add the ribeye steak and cook it for about 3 minutes on each side for medium-rare.
Remove from heat and let it rest for another 5 minutes.
Add butter to the same skillet.
Add garlic, thyme, and sliced onion.
Cook until the onion softens and becomes golden.
Toast the bread until golden brown and crispy.
You can use the oven or a toaster for this step.
Assemble the sandwich.
Place arugula, steak, onion, and tomato on one slice of bread.
Top with the other slice, and your sandwich is ready!