Bring butter to room temperature if needed. Spread 1/2 tbs butter on one side of each of 8 bread slices (the exterior-facing sides). On the interior-facing sides, spread 1 tsp mayonnaise on four slices and 1/2 tsp Dijon mustard on the other four slices. This creates a mayo layer on one inner slice and mustard on the other for each sandwich.

Season tomato and prepare avocado

Lightly salt and pepper the tomato slices with 1/4 tsp kosher salt and 1/4 tsp black pepper distributed evenly over slices. Toss the avocado slices gently with 1 tsp lemon juice and a pinch of salt to prevent browning and add brightness.

Assemble sandwiches

On the four mayo-spread inner slices, layer in this order: 2 oz (about 60 g) turkey per sandwich (divide 8 oz total), optional 1 oz ham if using, 1 slice provolone, tomato slices (2–3 per sandwich), avocado slices (about 1/4 avocado per sandwich), and 1 lettuce leaf. Top with the mustard-spread bread slice, buttered side out. Repeat for remaining sandwiches.

Grill or press (optional)

If you prefer warm or pressed sandwiches, heat a skillet or panini press over medium heat. Place assembled sandwiches buttered-side down on the skillet, press gently with a spatula (or close the press), and cook 2–3 minutes per side until golden and the cheese begins to melt. If using a skillet, flip carefully and cook the other side another 2 minutes.

Slice and serve

Transfer sandwiches to a cutting board and let rest 1 minute, then slice each sandwich in half on the diagonal. Serve immediately with optional quick pickles or chips.

Optional quick pickles & garnish

Make quick pickled onions while assembling sandwiches: combine 2 tbs apple cider vinegar, 2 tbs warm water, 1 tsp sugar and 1/4 tsp kosher salt in a small bowl. Stir until sugar and salt dissolve, add the 1/2 cup thinly sliced red onion and let sit at least 10 minutes (longer for a stronger pickle). Drain before using as a garnish on sandwiches.