Place cottage cheese in container of an electric blender or food processor; cover and process on high speed 30 seconds or until smooth, stopping once to scrape down sides.
Transfer to a small bowl.
Stir in watercress and next 5 ingredients.
Spread cheese mixture evenly over 5 slices of bread, and place tomato slices over cheese mixture.
Top with remaining 5 bread slices.
Transfer sandwiches to a sandwich press or hot griddle coated with cooking spray.
Cook until bread is lightly browned and cheese melts.