Heat a stove-top grill pan or griddle with cooking spray and set over medium-high heat. Spread soft herbed cheese on 4 slices of bread. Top cheese with pork, pickles, watercress, and Swiss cheese. Top with second slice of bread.
Brush bread with oil, place sandwiches on hot pan and weigh down with a baking sheet, top baking sheet with a heavy skillet to press down sandwiches. Cook for 2 minutes, until golden brown. Flip sandwiches using a spatula, topping with weighted baking sheet, and cook until second side is golden brown and cheese melts, about 2 minutes. Remove from heat and serve immediately.