Pat the chicken breasts dry with paper towels. If any breasts are very thick (over 1 inch), place them between two sheets of plastic wrap and gently pound with a meat mallet or heavy skillet to an even thickness about 3/4 inch. This ensures even cooking.

Make Marinade

In a medium bowl, whisk together olive oil, lemon juice, minced garlic, Dijon mustard, dried oregano, paprika, salt, and black pepper until combined.

Marinate

Place the chicken breasts in a resealable plastic bag or shallow dish. Pour the marinade over the chicken, turning to coat thoroughly. Seal or cover and refrigerate for at least 30 minutes and up to 4 hours. If short on time, marinate at room temperature for 15 minutes.

Cook & Finish

Preheat

About 10 minutes before cooking, remove the chicken from the refrigerator to come closer to room temperature. Preheat a large skillet (preferably nonstick or cast-iron) over medium-high heat for 2–3 minutes until hot.

Cook Chicken

Add 1 tablespoon olive oil to the hot skillet and swirl to coat. Remove chicken from the marinade, letting excess drip off, and place breasts in the skillet without overcrowding (work in batches if necessary). Cook undisturbed for 5–6 minutes until the underside is golden-brown. Flip and reduce heat to medium. Add 1 tablespoon butter to the pan; let it melt and spoon the melted butter over the breasts as they finish cooking for 4–6 minutes more. Cook until internal temperature reaches 165°F (74°C) when measured at the thickest part.

Rest

Transfer the cooked breasts to a cutting board and loosely tent with foil. Let rest for 5 minutes to allow juices to redistribute.

Slice & Serve

Using a sharp knife, slice the chicken breasts thinly against the grain into 1/4-inch slices. Arrange on a platter, sprinkle with chopped parsley if using, and serve with lemon wedges for squeezing over the slices.