In a bowl, paprika, cumin, chilli powder, salt, pepper, white sugar, brown sugar, and cayenne pepper. Apply it on both sides of tri-tip. Cover in cling wrap and refrigerate for at least 3 hours. (Refrigerate for about 3 days for intense flavours).
While the tri-tip marinates, blend lemon juice, mayonnaise, mustard, garlic, and rosemary in a bowl. Cover the tangy paste and refrigerate until needed.
Remove the tri-tip 1 hour prior to grilling it.
For grilling, preheat the grill to 500°F. Place tri-tip over direct heat for about 4 minutes on each side. Turn the burners to medium heat, close lid and cook for some time until internal temperature reaches 130°F to 140°F. Remove it from grill.
Let it rest for 10 minutes.
Slice the ciabatta into 1-inch slices and grill it in a little of the butter.
Layer one slice of ciabatta with the tangy paste, top it up with slices of tri-tip, provolone and arugula.
Stack it up with caramelized onions and topping of your choice. Your juicy tri-tip sandwich is ready!