Preheat oven to 425 degrees. Spread the sweet potatoes in an even layer on a baking sheet and drizzle with olive oil. Bake for about 15 to 20 minutes or until tender. Remove from oven and change the oven temperature to high broil.

Place the open kaiser roll buns on a clean baking sheet, sliced side of the bun facing up. Layer the sweet potatoes on the bottom buns, top with the beet, and finally place the feta cheese on top of the beets - making sure to divide each ingredient evenly between the bottom buns.

Broil for about 5 minutes or until the sliced side of the top bun and feta lightly begins to brown. Remove from oven and place the top bun on each panini and serve hot.