Finely grate the zest of the lemon, then cut the lemon inhalf. Heat 1 tablespoon oil in a large nonstick skillet over medium-highheat. Add the beef and cook, breaking it up with a spoon, untilbrowned, 4 to 5 minutes (spoon off and discard any excessfat). Add the garlic and 1⁄4 teaspoon each salt and pepper and cook,stirring, for 1 minute; toss with the lemon zest. Transfer thebeef to a bowl and squeeze the juice of half a lemon on top. Wash and dry the skillet, then heat the remaining tablespoon oil over medium-high heat. Add the rice and season with thecumin, coriander, and 1⁄4 teaspoon each salt and pepper. Cook, tossingoccasionally, until the rice begins to crisp at the edges, about5 minutes. Fold in the beef mixture and remove from heat. Meanwhile, squeeze the juice of the remaining lemonhalf into a medium bowl. Toss with the tomatoes, cucumber,scallions, and 1⁄4 teaspoon each salt and pepper. Fold in the mintand serve over the rice. Top with crumbled feta, if desired.