Place bacon slices in a cold skillet in a single layer. Cook over medium heat, flipping occasionally, until crisp (about 8–10 minutes). Transfer to a paper-towel-lined plate to drain. If desired, keep the skillet drippings for toasting the bread; otherwise discard.

Prepare the avocado

Halve the avocado, remove the pit, and scoop the flesh into a bowl. Lightly mash with a fork until mostly smooth with a few small chunks. Season with 1/4 tsp salt and 1/4 tsp black pepper and stir to combine. Reserve.

Toast the bread (optional)

Brush one side of each bread slice lightly with olive oil or spread butter (about 1/2 tsp per slice). Toast in a skillet over medium heat, or in a toaster, until golden and crisp, about 1–2 minutes per side in a skillet or 2–3 minutes in a toaster. Remove and place cut-side up on your work surface.

Mix the spread

In a small bowl combine mayonnaise (2 tbs) and Dijon mustard (1 tsp). Stir until uniform. Taste and adjust seasoning with a pinch of salt if desired.

Assemble the sandwich

Spread half of the mayo-mustard mixture evenly on one slice of the toasted bread and the remaining half on the other slice. On the bottom slice, layer the lettuce leaves first (2 leaves) to act as a moisture barrier. Place the sliced turkey (8 slices) evenly over the lettuce. Add the cooked bacon (4 slices) on top of the turkey. Spoon the mashed avocado (all) over the bacon and spread gently to cover. Arrange tomato slices (4) evenly, then add red onion slices (4). Top with pickle chips (4). Sprinkle the remaining 3/4 tsp salt and 3/4 tsp black pepper distributed lightly over tomato and avocado (use less if preferred). Close the sandwich with the top slice of bread, mayo-side down.

Finish and serve

Press the sandwich gently together, then cut in half diagonally. Serve immediately. If packing for later, keep avocado mashed separately and assemble just before eating to avoid bread sogginess.