In a medium pot, bring water to a boil and stir in couscous. Return to a boil, then reduce heat and simmer, covered, for 10 minutes. Drain any remaining water and set aside to cool.

Whisk together olive oil, lemon juice, salt and sugar.

Heat 4 tablespoons of the oil/lemon juice mixture in a small sauté pan; add garlic and heat for 30 seconds, stirring constantly, until fragrant. Add spinach to pan; stir until wilted and fully coated.

Fluff couscous with a fork and transfer to a large bowl. Combine couscous with garlic mixture and all remaining ingredients, except feta cheese; mix well and chill. Sprinkle with feta cheese before serving.