arugula, tuna & cannellini bean salad

It's hot out! This is the perfect healthy and hearty salad that requires little more than assemblage. I estimate we've made it about 75 times! No kidding.

1 package of arugula
2 cans of tuna packed in olive oil
1 can of cannellini (white kidney) beans, rinsed and drained
1-2 Tbsp of drained capers
1/4-1/2 diced red onion
Red or white wine vinegar
1 tsp of dijon mustard (optional)
Salt and pepper to taste

Assemble in a serving bowl:
Arugula
Drained tuna (reserve olive oil for dressing)
Beans
Capers
Red onion

For the dressing:
Drain the olive oil from the tuna into a small bowl
Add red or white wine vinegar to taste (no more than 1/4 the amount of olive oil; add more olive oil if needed)
Add dijon mustard and whisk dressing
Pour over assembled ingredients and toss

Here is my inspiration for this salad: http://www.foodandwine.com/recipes/tuna-and-white-bean-salad