Spread hummus on 1 side of each bread slice (about 1 ½ tablespoons each).
Top each of 4 slices in even layers with 2 tablespoons sun-dried tomatoes, ¼ cup cucumber, 2 tablespoons onion, ¾ cup spinach and 2 tablespoons feta.
Top with the remaining 4 slices, hummus-side down.
Cut the sandwiches in half diagonally and serve.
