1 medium sweet onion, such as Vidalia, finely chopped
3 tablespoons finely chopped fresh spearmint
Preheat the oven to 350°. Put the beets in a baking dish and toss with 2 tablespoons of the oil. Cover with foil and bake for about 1 1/2 hours, or until tender when pierced with a knife. Let cool slightly, then slip off the skins. Cut into 1-inch cubes.
Meanwhile, put the bulgur in a medium bowl and pour the boiling water over it. Cover with a plate and let stand until the water is absorbed and the bulger is tender, about 1 hour. Drain the bulgur, rinse with cold water and squeeze dry in handfuls, fluffing it with your fingers as you transfer it to a large bowl.
In a small skillet, toast the allspice and cumin over moderately high heat until fragrant, about 1 minute. Let cool. Grind in a spice grinder or mortar, or finely chop with a knife. Transfer to a bowl. Add the remaining 1/4 cup plus 1 tablespoon olive oil, the lemon juice, 1/2 teaspoon salt and a generous pinch of pepper.
Add the dressing and the onion to the bulgur, toss well and season with salt and pepper. Add the beets and toss again. Stir in the spearmint and serve chilled or at room temperature.
The tabbouleh can be refrigerated for up to 1 day.