Preheat oven to 400 degrees. Seal beets in a foil packet. Roast on a rimmed baking sheet until tender, 75 minutes. When cool, rub beets with a paper towel to remove skins; slice. Slice large tomatoes, and halve cherry tomatoes, then arrange with beets on a platter. Top with feta, cilantro, and olive oil; season with salt and pepper.