Pound each chicken breast to an even thickness (about 3/4 inch) using a meat mallet or heavy skillet wrapped in plastic wrap. This ensures even cooking and tender results.

Season

In a small bowl, mix salt, black pepper, garlic powder, and paprika. Lightly brush both sides of the chicken breasts with olive oil, then sprinkle the seasoning mix evenly on both sides.

Cook chicken

Heat a grill pan or skillet over medium-high heat until hot. Add a small drizzle of oil or spray. Cook the chicken breasts 4 to 6 minutes per side (depending on thickness) until an internal temperature of 165°F (74°C) is reached and the exterior is nicely browned. Remove from heat and let rest 3 minutes.

Melt cheese

Place one slice of American cheese on each cooked chicken breast while still hot. Cover the pan briefly with a lid (30–60 seconds) or tent with foil to let the cheese melt.

Toast buns (optional)

Spread softened butter on the cut sides of the sandwich buns. Toast cut-side down in a clean skillet over medium heat until golden, about 1–2 minutes.

Prepare produce and condiments

While chicken rests, wash and dry lettuce leaves. Slice the tomato into 1/4-inch rounds. If pickles are whole, slice into 6 thin rounds. In a small bowl, mix mayonnaise and mustard until combined.

Assemble

Spread about 1 tablespoon of the mayo-mustard mixture on the bottom half of each toasted bun. Place the lettuce on the sauced bottom bun, then add the tomato slices, then the cheesy grilled chicken breast. Top the chicken with pickle slices. Spread remaining sauce on the top bun and close the sandwich.

Serve

Slice the sandwich in half if desired and serve immediately while the chicken and cheese are warm.