In a medium bowl, combine olive oil, lemon juice, minced garlic, paprika, oregano, salt, and pepper.

Place chicken breasts between two sheets of plastic wrap and gently pound to an even thickness of about ½ inch using a meat mallet or heavy pan. This ensures even cooking.

Add chicken to the marinade, turning to coat completely. Cover and refrigerate for at least 30 minutes (or up to 4 hours for more flavor).

If you're short on time, you can skip the marinating step and simply season the chicken with salt, pepper, and paprika before cooking, but the extra time yields much more flavorful results.

Heat a grill pan or skillet over medium-high heat. Add a small amount of oil to prevent sticking.

Remove chicken from marinade, letting excess drip off, and place on the hot grill pan.

Cook for 5-6 minutes on each side, or until the internal temperature reaches 165°F (74°C) and the chicken is no longer pink inside.

Transfer to a cutting board and let rest for 5 minutes before slicing across the grain. This resting period keeps the juices inside the meat.

Cut avocados in half, remove the pit, and scoop the flesh into a medium bowl.

Add lime juice, cilantro, minced garlic, and red pepper flakes if using.

Mash with a fork until you reach your desired consistency – I prefer to leave some small chunks for texture.

Season with salt and pepper to taste.

Toast the bread slices until golden brown.

Spread a thin layer of mayonnaise on one side of each piece of bread.

On two of the bread slices, generously spread the avocado mixture.

Layer on the sliced chicken, then add tomato slices, red onion, and greens.

Top with the remaining bread slices, mayo side down.

Cut diagonally and serve immediately.