Scrub potato skins and dry well. Score the top of each potato in an X shape. Rub each potato with about 1/2 tablespoon olive oil and sprinkle with kosher salt. Place directly onto the grill grates of a 375° preheated pellet grill or place on a large baking sheet and bake in the oven. If baking on a charcoal grill, wrap potatoes in foil. Bake until fork tender, about 1 hour or until potatoes reach about 200° using an instant read thermometer. Remove from grill and set aside.
Pat chuck roast dry with paper towels and place on a rimmed baking sheet. Drizzle with about 1 tablespoon of olive oil and sprinkle with 2 tablespoons steak rub on each side.
Prepare a charcoal grill fire to 350° using hickory or oak for smoke flavor. We are using lump charcoal and our oak premium cooking wood on the Big Green Egg ceramic grill.
Place chuck roast onto the grill grate and cook with the lid closed about 10 minutes.
Flip the roast and close the lid, continue to cook until roast reaches desired doneness. We cooked ours to about 130°. The roast will continue to cook when the potatoes are assembled.
Remove roast to a cutting board and rest for 15 minutes. Slice into thin strips and chop into bite-sized pieces.
Remove potatoes from grill and place on a sheet pan. Line the baking sheet with parchment paper or aluminum foil if desired. Use a cast iron skillet or a potato masher to smash potatoes flat.
Drizzle potatoes with about 1/2 tablespoon olive oil or use melted butter if desired. Sprinkle with 1 - 2 teaspoons steak rub. If you want crispy edges, place under the broiler for about 5 minutes until edges start to brown.
Top with shredded cheese and chopped roast beef. Sprinkle with more steak rub if desired.
Return to the grill or place under an oven broiler for 5 minutes or until cheese is melted.
Top with salsa fresca.
Serve with sour cream and cilantro.