Prepare the Tri-Tip by carving off any large fat areas, then generously coat/rub with the garlic powder and salt on both sides. Let set for 15 minutes.
Place in a ziplock bag (or a dish) and add Teriyaki sauce ensuring to cover all parts of the Tri-Tip. Seal and set in refrigerator for 2 hours or longer. Over night is even better!
Heat grill to a medium high temperature and sear on one side for 5 minutes, turn and sear for 6 - 8 minutes on the other side. This helps to seal and hold moisture.
Move the Tri-Tip to an area of your grill without direct heat and adjust so that the temperature with the lid closed is about 400 degrees. Grill with indirect heat for about 25 minutes until the Tri-Tip internal temperature reaches 130 - 135 degrees.
Remove from the grill and cover allowing the Tri-Tip to rest for 10 - 15 minutes before carving with the grain of the meat.
Preheat oven to 400 degrees.
Note: I often cook this on my outdoor grill when I will be grilling meats like tri-tip or steaks, which will give it more of a smokey flavor. Just cook it on a side of your grill with indirect heating and the temp to about 400 degrees.
Thinly slice both onion halves and the potatoes. Cut them about as thin as you can. If you have thick chunks of potatoes, you may have to increase cooking time.
Now we will build layers in a cast iron skillet by adding 2 oz olive oil to the bottom of the pan, layer in half of the onions, then layer on half of the potatoes, then half of the bacon. Add salt and pepper to taste, then 1 oz olive oil distributed on top. Then more layers with the remaining onions, potatoes and bacon. Again salt and pepper to taste.
Bake for 30 minutes at 425 degrees.
Add cheese evenly around the top, lower temperature to 350 and bake another 20 minutes until the cheese is melted.
Remove from oven and cover with aluminum foil or other lid. Covering will help it to not dry out while you are getting ready to serve.
Caution, the cast iron skillet will be very hot, please take precautions so that you and others that may be nearby do not touch without proper protection!