If you don't have orzo use any small pasta shape - macaroni, small conchiglie, anything really just small shapes.
You can add bacon when cooking the onion for a variation, you can stir through parsley just before serving, you can leave out the pasta for just a tomato soup - lots of variations.
If you don't have Gruyere use a strong hard cheese, I used cheddar the other day mixed with a bit of Jarlsberg I had left. I also didn't have any white bread so I used the end of an old baguette, just make those croutons cheesy!
Adapted from a recipe from the Barefoot Contessa