Put the bulgur in a small bowl, cover with hot water and soak until softened, about 1 hour. Strain and set aside.
Toss the cucumbers, tomatoes, half the mint, 1 tablespoon of the oil, lemon juice, 1/2 teaspoon salt and 1/4 teaspoon pepper in a medium bowl; cover and refrigerate until ready to serve.
Preheat the oven to 400 degrees F. Spray an 8-inch square baking pan lightly with cooking spray and set aside.
Pulse the onions into a paste in a food processor, scraping down the bowl as needed. Heat the remaining 2 tablespoons oil in a large nonstick skillet over medium heat. Add the onion paste and any onion juice and cook, stirring occasionally, until the paste begins to brown (it will still be light), about 10 minutes. Add the cumin, cinnamon, allspice, 1 1/2 teaspoons salt and a few grinds of pepper and continue cooking until the onion-spice paste starts to look dry and is fragrant, 4 to 6 minutes.
Add the onion-spice paste, bulgur, ground beef, egg, breadcrumbs, remaining chopped mint, 1/2 teaspoon salt and several grinds of pepper to a large mixing bowl and mix with your hands until thoroughly combined. Press the mixture into the prepared baking pan; sprinkle with the pine nuts if using and press in. Bake until the meatloaf begins to pull away from the sides, is browned on top and registers 165 degrees F on an instant-read thermometer, 30 to 35 minutes. Slice the meatloaf into 1-inch-thick slices and serve hot with the cucumber-tomato salad and dollops of Greek yogurt alongside.
Copyright 2013 Television Food Network, G.P. All rights reserved.