Ingredients

2 tablespoons plain low-fat yogurt 

1 to 2 teaspoons Dijon mustard 

1 tablespoon fresh lemon juice 

Coarse salt and ground pepper 

3 ounces baby spinach (about 3 cups, loosely packed) 

1/2 cup seedless red grapes, halved lengthwise 

1/4 cup thinly sliced red onion (optional) 

1 can (3 ounces) chunk light tuna packed in water 

Flatbreads, for serving (optional) 

Preparation

In a small bowl, whisk together yogurt, Dijon, and lemon juice; season with salt and pepper. Place dressing in a resealable plastic bag or airtight container. Place spinach, grapes, and onion, if using, in another airtight container (separate from dressing). Refrigerate, up to overnight.

Just before serving, drain tuna, add to salad, and toss with dressing. Include flatbreads, if desired.