In a medium mixing bowl, mash the ripe avocado until mostly smooth. Add mayonnaise and sour cream (or Greek yogurt). Stir in finely chopped fresh chives, dill, and parsley. Add minced garlic (or garlic powder), onion powder, dried mustard, and fresh lemon juice. Season generously with salt and freshly ground black pepper, and a pinch of cayenne pepper if desired. Stir thoroughly until well combined and creamy. Cover and refrigerate for at least 30 minutes to allow flavors to meld.
Pound the chicken breasts to an even 1/2-inch thickness between plastic wrap. Pat dry and season generously with salt and pepper. Heat 2 tablespoons olive oil in a large skillet or grill pan over medium-high heat. Cook chicken for 4-6 minutes per side until golden brown and cooked through (internal temperature should reach 165°F/74°C). Transfer to a cutting board and let rest for 5-10 minutes before slicing against the grain into thin strips.
Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper or foil, optionally using a wire rack. Arrange beef bacon slices in a single layer. Bake for 15-20 minutes, or until golden brown and delightfully crispy, monitoring closely. Transfer cooked bacon to a paper towel-lined plate to absorb excess grease and cool.
Wash the lettuce thoroughly and pat dry. Slice the ripe tomatoes into thin, even rounds. For the red onion, thinly slice it (soaking it in ice water for a milder flavor if desired). Have your cheese slices ready to go.
Toast three slices of bread per sandwich until golden brown and slightly firm. Lay out the first slice of toasted bread and generously spread avocado ranch on it. Layer with crisp lettuce and thinly sliced tomatoes (season these with salt and pepper). Then, arrange half of the sliced chicken breast over the tomatoes, followed by 3-4 slices of crispy beef bacon and two slices of cheese. Take the second slice of toasted bread and spread avocado ranch on both sides. Place it spread-side-down onto the cheese layer and repeat: avocado ranch, lettuce, seasoned tomatoes, remaining chicken breast, remaining crispy bacon, and optionally red onions. Finally, take the third slice of toasted bread, spread a generous layer of avocado ranch on its bottom side, and place it spread-side-down on top of all the fillings. To secure everything, insert two long wooden toothpicks or skewers diagonally through the sandwich. Using a sharp serrated knife, carefully slice the sandwich in half (or into quarters, creating triangles) along the line of the toothpicks. Serve immediately.
Notes
Perfect for a hearty lunch or dinner. Pairs well with a light salad or sweet potato fries.