Cover bottom of the au gratin pan in olive oil. Peel sweet potatoes and cut them into pieces slightly larger than bite-sized. Place pieces in pan and cover in olive oil. Salt and pepper to taste.
Bake sweet potatoes for 40 minutes at 375F/190C or until soft.
Add half can of black or pinto beans (mostly or completely drained) and place back in oven for 10 minutes.
Add cold, halved grape tomatoes and avocado. Serve in au gratin pan for a beautiful dish and to keep all the flavors together.