As one of my friends likes to say, this salad is "cute as hell." I won't lie, it is. But more importantly, I love cannellini beans, and there's no easier way to enjoy them than in this good-looking, great-tasting salad. Even though the beans are from a can they should still be firm and whole, not all mushy and falling apart. If you open a can and the beans look like that, then you need to be using another brand of beans. The thinly sliced red onion adds a nice bite as does the spicy arugula. Make sure that the arugula you get looks really perky and green.
Shake the olive oil, vinegar, chopped basil, salt and pepper in a sealable container until the salt is dissolved. Pour the dressing over the salad and toss well. It's best to make and dress the salad about an hour before you serve it. Let it stand at room temperature, tossing every time you think about it. Just before serving, adjust the seasoning with salt and pepper, to taste.