Preheat grill to about 225. If you're using a charcoal grill feel free to add a chunk of hickory or oak wood. Trim tri tip so that there is only about 1/4 inch of fat on the fatty side. Coat with salt pepper and garlic powder and place over indirect heat. Barbecue until internal temperature is 120 F.
While Tri tip is cooking, slice bell pepper and onions and place in a skillet with a little olive oil. Cook on the grill when tri tip is about 10 minutes away from being done.
When trip tip hits 120 F, take it off the grates and turn grill hit up to highest heat settings for searing. If using charcoal add open up the vents to get the heat going. Place tri tip over direct heat and seat about 2-3 minutes per side until you have the color you want or until the internal temperature is 135 F. Let rest for 5 minutes.
Slice tri tip thinly against the grain, place in a hoagie roll with cheese and onions and peppers. Place in a broiler or back in the grill to melt cheese. Enjoy!