We pre-heat our gas grill.
While the chicken is grilling, we cover our grilling brick with heavy duty aluminum foil.
We cut our bread in half lengthwise, and then each half in half for four good-sized sandwiches.
When the chicken is cooked, we slice each piece in half lengthwise. We coat each sandwich with 1 tablespoon of pesto, spreading it on both sides of the bread. We top with some tomato and cheese, the chicken, and some of the spinach leaves. When all the sandwiches are made, we put them on the grill, two at a time, weighting them down with the brick facing the open sides of the sandwiches so as to try and keep the ingredients inside. We cook for a few minutes on the one side, carefully remove the brick, flip the sandwiches, and weight again. We keep them on the grill until the crust is toasty and the cheese is melted. We repeat with the remaining sandwiches and serve.