Preheat your grill to high, around 500°F. Prepare for direct and indirect grilling by only using one or two burners, while leaving the others off.
Season your steak with the steak spice and leave it to sit while the grill comes up to temperature.
Season the tomato slices to taste with salt and pepper. Sprinkle with oregano.
Sear the steak over direct heat for one to two minutes, turn the steak 45° clockwise and leave it another minute. Flip and repeat. Remove the steak from the grill and allow it to rest under foil for 10 minutes before slicing. You want to keep the steak on the medium rare side because it will cook further once on top of the pizza.
Turn the grill down to medium-low, around 325°F to 350°F.
Top the focaccia with the sliced tomatoes, slices of steak, and onions. Sprinkle with the shredded cheese. Place the pizza over indirect heat, right on the cooking grids and close the lid.
Grill for 10 to 20 minutes, or until the cheese has melted and the tomatoes are all roasty and delicious (trust me you’ll know). Remove the pizza from the grill and slice.