Preheat oven to 400°. Prepare the chicken breasts by either steaming or cooking in a non-stick frying pan without fat. Then, let them cool.
Arrange the slices of bread on a baking dish. Spread generously with Brie and bake for 2 min.
Cut the chicken into strips and arrange them on the 4 slices of toasted bread. Sprinkle the chives over all the chicken strips. Bake again for 3 to 4 min (brown bread should not blacken).
Cut the cherry tomatoes in half and put them in a bowl. Drain the soft corn. Add to salad. In a bowl, mix the mustard, yogurt and vinegar. Coat the salad with this dressing.
Serve the croque monsieur chicken and Brie sandwiches with the salad.