Combine first 8 ingredients in a food processor; process until smooth.
Spread 2 Tbsp hummus over 1 bread slice; top with 1/2 cup lettuce, 2 tomato slices, 1 onion slice, 1 bread slice, 1/4 cup cucumber, 1 cup sprouts, and 1 bread slice.
Cut sandwich diagonally into quarters; secure with wooden picks.