Slice steak into 1/2 inch strips using a sharp knife. Place in a zip top bag.
Add marinade ingredients to a bowl: olive oil, lime juice, brown sugar, garlic, chili powder, cumin, salt, pepper and smoked paprika. Whisk until well combined.
Pour marinade over the sliced steak. Press out excess air and seal the bag. Turn over several times until steak is well coated in the marinade. Refrigerate at least one hour and up to 4 hours.
Slice bell peppers and onions and set aside or refrigerate until ready to grill.
Scrub potatoes and dry well. Using a sharp, pointed knife, cut an X shape in the top of each potato.
Prepare a grill fire to 400°. Cook the potatoes on a piece of heavy duty aluminum foil if cooking over direct fire. If you are using a pellet grill, foil is optional. Cook potatoes until the internal temperature reaches 200° using a digital thermometer.
Remove potatoes from the grill and keep warm.
Cool the grill down to about 350°. Place a grill basket, grill pan or griddle onto the grill. Add the marinated steak, peppers and onions.
Stir to combine and cook with the grill closed. Stir every 5 minutes, cooking until steak is cooked through and vegetables are softened.
Remove from the grill and set aside.
Cut potatoes in half lengthwise. Place onto a aluminum foil lined baking sheet and smash flat using a spatula or potato masher.
Scrape the potato flesh and add a pat of butter, mixing the butter into the potato as it melts. Season with sweet bbq rub or your favorite all purpose seasoning. Top with shredded cheese.
Top each potato with beef fajita mixture.
Return to a hot grill or place under the broiler for 2-3 minutes or until cheese is melted.
Serve potatoes with salsa fresca and sour cream.