Place a baking rack on a sheet pan and lay the bacon on the rack. Roast for 15 to 20 minutes, until browned. Remove to a plate lined with paper towels.
Meanwhile, prepare the guacamole. Place the avocados, lime juice, scallions, red onion, jalapeno pepper, garlic, 1 teaspoon salt, and 1/2 teaspoon pepper in a mixing bowl and mash roughly together with a fork. Taste for seasoning; it should be very highly seasoned. Set aside.
When the bacon is done, heat a dry cast-iron skillet over high heat for 5 minutes. Pat the salmon fillets dry with paper towels, brush them all over -- top and bottom -- with olive oil, and sprinkle generously with salt and pepper. Place the fillets in the skillet skin side up and allow them to cook without disturbing them for 2 minutes exactly. With a metal spatula, carefully turn the fillets and cook for 2 more minutes. Transfer the skillet to the oven for 2 minutes (time it carefully!). Remove the salmon to a plate and cover it tightly with aluminum foil. Allow it to rest for 10 minutes.
While the salmon rests, cut the ciabatta rolls in half crosswise, place them cut side up on a sheet pan, and toast in the oven for 5 to 10 minutes, until lightly toasted.
To assemble the sandwiches, place the bottoms of the ciabatta rolls on a board and spread each with 2 rounded tablespoons of guacamole. Remove the skin from the salmon fillets, cut each fillet in half crosswise, and place both halves on top of the guacamole. Add 2 slices of bacon, a handful of arugula, and a sprinkling of salt. Spread another rounded tablespoon of guacamole on the underside of the top bread and place on top. Continue arranging all the sandwiches. Cut each sandwich in half diagonally and serve warm or at room temperature.