Step 1
Place each chicken breast between two pieces of foil, plastic wrap, or wax paper. Pound the breasts with a mallet or the bottom of a heavy pan or mug, to thin.
Step 2
Season chicken breasts evenly and on both sides with garlic, oregano or Italian seasoning, salt substitute and black pepper.
Step 3
Add 1 ½ Tablespoons of oil to an 8" skillet and tilt the pan so the oil coats the bottom of the pan. When shimmering, add the chicken so both pieces are flat and not overlapping. Cook for 5 minutes on each side, or until golden and cooked through. Then remove chicken from the heat.
Step 4
When cool enough to handle, slice the chicken into thin strips, about ¼" thick.
Step 5
Spread 1 Tablespoon of pesto across all 8 slices of bread.
Step 6
Divide greens (if using) amongst 4 slices of bread, then the tomatoes, then the chicken, and finally the mozzarella on top. Form a sandwich by adding the other slices of bread on top.
Step 7
Heat a clean skillet to medium high, and spray with oil spray or add ½ Tablespoon oil. When the oil is hot (but not smoking), add the sandwiches 2 at a time and place a heavy bottomed skillet on top to press the sandwiches. Cook about 30 seconds, then carefully flip to toast the other side. Adjust heat as needed so as not to burn the sandwiches, but to allow the cheese to melt and the bread to turn golden and crispy.
Step 8
Remove the sandwiches from the skillet and repeat with the remaining sandwiches.
Step 9
Cut sandwiches in half on the diagonal, and serve while hot.
*This sandwich is already high in sodium due to the cheese, the bread, and the pesto. Opt for a salt replacement to season the chicken, or skip the salt in order to keep the sodium content of the meal within a healthy range.