Brick Chicken

Ingredients:
2 tablespoons canola oil
1 (3 to 4 pound) chicken, halved, backbone, rib cage, and thigh bones removed
Coarse salt and freshly ground black pepper
1 tablespoon freshly squeezed lemon juice
1/3 cup homemade or store-bought, low sodium chicken stock
Thinly sliced heirloom tomatoes, for serving