Preheat oven to 375°F Place beets, cut sides up, on parchment-lined foiled rimmed baking sheet.
Drizzle with oil oil and sprinkle with 1/4 teaspoons salt. Fold foil over beets to enclose and crimp edges to seal. Bake until tender, about 35 minutes. (Beets can be refrigerated in an airtight container overnight.).
Arrange beets and tomatoes on a serving platter. Drizzle with oil and lemon juice, and season with remaining 1/4 teaspoons salt and pepper. Scatter mint over top and serve.