1 small head green leaf lettuce, torn or cut into bite-sized pieces
1 small head red leaf lettuce, torn or cut into bite-sized pieces
1 orange, yellow, or red bell pepper, thinly sliced
1/2 seedless cucumber, quartered lengthwise and sliced
1 cup cherry tomatoes, halved or quartered if large
1/4 cup thinly sliced red onion
1 tablespoon Champagne vinegar
1/2 teaspoon Dijon mustard
3 tablespoon extra-virgin olive oil
Kosher salt and freshly ground black pepper