Cover a baking tray with paper towels. Lay cucumber slices on top and sprinkle with salt. Set aside for 5 minutes to draw out moisture. Transfer to a small bowl. Add vinegar and set aside to pickle for 10 minutes. Drain.
Meanwhile, place couscous and ½ cup boiling water in a heatproof bowl. Cover with tea towel and set aside for 5 minutes or until water has absorbed. Using a fork, fluff up couscous. Add tomato, parsley, lemon zest and juice, gently stirring to combine. Season with freshly ground black pepper.
Heat falafels in microwave for 45–60 seconds or until warm.
Place one pita bread on each serving plate. Spread with hummus, then serve topped with couscous, falafels, pickled cucumber and baby spinach.