You can make the salad and the dressing in advance. Remember to mix the two only when you are going to have the salad.
If you do not like the sharp taste of onions meddling with the other ingredients, here's a tip to dial it down. Mix salt and a tablespoon of lime juice in a bowl of warm water and soak the onion slices for about 10 minutes. Rinse and add the onions to your salad.
You can play with the ingredients to make your own salad. For example, you can add lettuce and bell pepper in place of onion and arugula for a different flavor.
Roasted pumpkin seeds or peanuts are also a good way to bring up the protein levels in your salad.