In a medium bowl, toss the shredded chicken with 1 tablespoon yellow mustard, 1 teaspoon olive oil, 1/2 teaspoon kosher salt, 1/4 teaspoon garlic powder and 1/4 teaspoon black pepper until evenly coated. Taste and adjust seasoning; add up to 1–2 teaspoons additional mustard if you prefer a more pronounced mustard flavor.

Assemble sandwich

Split the ciabatta or focaccia loaf horizontally into top and bottom halves. If the loaf is very thick, cut to make two sandwich-sized halves.

Lightly spread the bottom half with the mayonnaise (about 1 tablespoon) to add richness and to protect the bread from becoming soggy.

Distribute the seasoned chicken evenly over the bottom half of the bread in a single, even layer.

Dot or thinly brush 2 tablespoons yellow mustard across the chicken layer in an even layer so mustard is present in every bite.

Top the mustard-coated chicken with the provolone slices, arranging them so they overlap slightly and fully cover the chicken (use 3–4 slices depending on loaf size).

Add optional garnishes now if using: a quarter cup sliced pickles, pickled red onions, and/or 1/2 cup arugula. These should be placed on top of the cheese.

Place the top half of the loaf over the assembled ingredients. Spread the top bread exterior with the softened butter (about 1 tablespoon) to help achieve a crisp, golden crust when pressing and to add flavor.

Press and finish

Preheat a sandwich press/panini press to medium-high. If you don't have a press, heat a large skillet over medium-high and have a heavy skillet or foil-wrapped brick ready to press the sandwich.

If using a panini press: place the assembled sandwich in the press, close, and cook for 4–6 minutes until the bread is golden and crisp and the provolone is melted. If using a skillet: place the sandwich in the hot skillet, then place the heavy weight on top. Cook 3–4 minutes on the first side until golden, then carefully flip and press the other side for another 2–4 minutes, until cheese is melted and bread is evenly crisped.

When done, remove the sandwich from the press and let it rest 1–2 minutes to settle. This prevents juices from making the bread soggy and makes slicing cleaner.

Slice the pressed sandwich into portions (2–4 pieces depending on loaf size) using a serrated knife and serve immediately.

Notes

To save time, use rotisserie chicken or leftover roasted chicken. For a tangier Cinerama, increase yellow mustard to taste. For a darker, crispier crust, brush the exterior of both bread sides with olive oil instead of butter before pressing.