1 large romaine lettuce heart, cut into bite-size pieces
1 small seedless cucumber, thinly sliced
Preheat the oven to 350°. On a baking sheet, toss the bread cubes with 1 tablespoon of the olive oil and toast for about 10 minutes, stirring once, until golden. Let the croutons cool.
In a large bowl, whisk the mustard with the balsamic vinegar. Gradually whisk in the remaining 3 tablespoons of olive oil and season with salt and pepper. Add the romaine, cucumber and croutons, toss well and serve.
The croutons can be stored in an airtight container at room temperature for up to 1 week.