1. Preheat oven to 425 degrees. Place beets on a large piece of foil on a baking sheet. Top with 2 teaspoons oil and season with salt and pepper. Fold foil around beets and crimp ends to form a packet. Roast beets on sheet until tender when pierced with a knife, 45 minutes to 1 hour. Remove beets from foil and let cool, then peel and cut into 1/4-inch-thick slices.

2. In a small bowl, whisk together remaining 3 teaspoons oil, shallot, and vinegar; season with salt and pepper. On a large platter, arrange beets and tomatoes, and season with salt and pepper. Drizzle with dressing and sprinkle with fresh oregano leaves.