Clean three bunches of cilantro by soaking and rinsing in a salad spinner until the water runs clear; dry well in the spinner.
Wash two bunches of scallions, remove the root ends, and roughly chop.
Wash two bunches of chives and chop into small pieces.
Prepare two jalapenos: for a spicy sauce include ribs and seeds, for mild use only the flesh; roughly chop.
Extract about 3/4 to 1 cup of lime juice from 3–4 juicy limes; keep the juice cold.
In a blender or food processor add about half of the lime juice and blend the cilantro, scallions, chives, and jalapenos until pureed and broken down.
Add the remaining lime juice (adjust for acidity), 1/2 to 1 cup avocado oil, 1/2 cup avocado mayonnaise, 1–2 tbsp agave nectar, and salt to taste; blend until smooth.
Optionally add 1/2 an avocado for more color, flavor, and creaminess; blend again until combined.
Taste the cilantro sauce and adjust seasonings (salt, agave) so the sauce is cilantro-forward, limey, spicy, and creamy.
Cook bacon strips by placing them on a sheet tray in a cold oven, turning the heat to 375°F (190°C) and cooking for about 30 minutes or until crispy; flip and rotate occasionally. Once cooled, chop into bite-sized pieces and reserve any bacon fat.
Grate Fontanella cheese as finely as possible using a small grater.
Assemble your station with sliced avocado (if using), sourdough bread, chopped bacon, grated Fontanella cheese, and the cilantro sauce.
On two slices of sourdough bread distribute about 1/2 cup of grated Fontanella cheese evenly (add more if desired for extra cheesiness).
Add a thin layer of chopped bacon over the cheese to ensure a few pieces in every bite.
Slice 1/4 of an avocado thinly and lay a thin layer on top of the bacon.
Be liberal with the cilantro sauce, spreading it over the avocado so it penetrates the sandwich without spilling excessively out the sides.
Carefully close the sandwich quickly and intentionally to keep the cheese from running out.
Preheat a cast iron pan on low until heated through, then increase to medium for cooking.
Place the sandwich dry (no fat) in the well-preheated pan at medium heat to toast the bread and make it crisp and sturdy; manage heat to avoid burning.
Once one side is lightly toasted, flip the sandwich and spread a very thin coating of mayonnaise on the toasted side of the bread from edge to edge (mayo has a higher smoke point than butter).
When the bottom side is nicely golden, flip again and add a thin coating of mayonnaise to the other side.
Once both sides are golden brown, lower the heat and continue flipping the sandwich every ~30 seconds to prevent further browning while allowing the cheese to fully melt.
When the cheese is fully melted, the sandwich is done—serve immediately, optionally with your favorite hot sauce.
