Spread Hummous on one slice of bread. Spread avocado on the other slice (general technique: slice a circular slice, or just scoop out, and then use fork to mash avocado down; if it's really hard avocado, use a good knife to cut it into tiny cubes and then mash. Then the mashed avocado can be scooped onto the bread, and spread with a knife).
Chop green onion and sprinkle on one slice, chop peeled (or washed and scrubbed) cucumber (best: pickling cucumbers) on the other slice (I suppose that if I were a True connoisseur, I would care which slice, with which spread, one puts the green onions and on which one puts the cucumbers... But I'm not. Looking down at the sandwich I have now, I see I've put the cucumbers on the avocado side and the green onions on the hummous. I suppose esthetically, the light green of the cucumber slices looks nicer on the darker green of the avocado than would the similarly dark green slices of green onion. There you have it, that should satisfy you Connoisseurs out there).
Now add nice big slices of juicy ripe organic tomato in the middle. To get a nice thick and moist sandwich, add a slice or several of firm tofu in the middle.
Your sandwich awaits, ready, willing, able, and eager to please. (Ok, so I'm getting a little carried away. But these sandwiches, yes I'm eating while typing again, are *good*).
Some things you might want to add or substitute for variation: