Step 1: Smoke the Tri-Tip

• Prepare the Tri-Tip: If you’re starting with fresh tri-tip, begin by preheating your smoker (preferably a Traeger or pellet smoker) to 225°F.
• Season the Meat: In a small bowl, combine kosher salt, black pepper, brown sugar, smoked paprika, cayenne powder, onion powder, and garlic powder. Rub this seasoning mixture generously all over the tri-tip. Let it marinate for at least 30 minutes in the fridge to allow the flavors to penetrate the meat.
• Smoking the Tri-Tip: Place the seasoned tri-tip on the smoker and cook for about 2 hours or until the internal temperature reaches 125°F for medium-rare. Once done, remove the tri-tip from the smoker and let it rest for 10-15 minutes. Resting allows the juices to redistribute, ensuring a juicy and tender result.

Step 2: Prepare the Chimichurri Sauce

• Combine the Ingredients: For the chimichurri, place garlic cloves, fresh mint, parsley, cilantro, oregano, and red onion in a food processor. Pulse until everything is well combined but still chunky—don’t turn it into a paste.
• Add Oil and Vinegar: Drizzle in the olive oil and red wine vinegar. Pulse a few more times to combine. Adjust the oil to reach your desired consistency (less oil will create a more textured sauce, while more will create a smoother finish).
• Season: Add kosher salt and freshly ground black pepper to taste. Transfer the chimichurri to an airtight container and refrigerate until you’re ready to assemble the sandwiches.

Step 3: Sauté the Red Onions

• Caramelizing Onions: Heat a Blackstone griddle or a medium skillet to medium-high heat. Add the sliced red onions and sauté until they turn a deep golden brown and become tender. This should take about 20-30 minutes. If using a Blackstone, place the onions on the cooler side of the griddle to prevent burning.

Step 4: Toast the Ciabatta Rolls

• Toast the Buns: While the onions are caramelizing, slice the ciabatta rolls in half and butter both cut sides. On a flat top griddle or in a skillet, toast the rolls until golden brown. If you don’t have a Blackstone, you can also toast them under a broiler for about 2-3 minutes, or use an air fryer.

Step 5: Slice the Tri-Tip

• Slicing the Meat: After the tri-tip has rested, slice it thinly across the grain. Slicing against the grain ensures that each bite is tender and easy to chew. The thickness of the slices is up to you—some prefer thicker slices for more bite, while others opt for thin slices for more delicate mouthfuls.

Step 6: Assemble the Sandwiches

• Assemble the Sandwiches: Spread a generous layer of creamy horseradish sauce on the bottom half of each toasted ciabatta roll. Then, lay down a layer of the sliced tri-tip, followed by the caramelized onions.
• Add the Cheese: Top each sandwich with two slices of provolone cheese. If you’re using a Blackstone griddle, cover the sandwiches with a basting dome and place some water underneath to help melt the cheese. Alternatively, you can place the sandwiches under the broiler for 1 minute or use an air fryer at 400°F for about 2 minutes to melt the cheese.

Step 7: Add the Chimichurri Sauce

• Final Touches: Spread about 2 tablespoons of chimichurri sauce on the top half of each toasted ciabatta roll. This fresh, herby sauce adds a vibrant contrast to the richness of the tri-tip and cheese.
• Assemble and Serve: Join the two halves of the sandwich, pressing them together gently. Slice the sandwiches in half to reveal the juicy, cheesy goodness inside, and serve immediately.