Classic combination this, but when asparagus is in season it's a lovely light lunch to base around a handful of asparagus. Serves 2, takes 10 minutes, and NB it involves a raw egg so it's not for anyone preganant.
Put a griddle pan on a high heat to warm up. Put the bread in the toaster on a light setting. (The plan is to ignore when it pops up and leave it in the toaster while preparing the other stuff, which gets the bread a bit dry and crispy which complements the other stuff well.) Separate the egg, putting the yolk in a small mixing bowl, and put the white in the fridge/freezer (we don't need it). Shave/slice the cheese finely.
Put the asparagus in the hot griddle pan (lying perpendicular to the lines of the pan). Sprinkle a small amount of oil onto the asparagus. Let it cook for 5--7 minutes or so, turning halfway through, and meanwhile make the mayonnaise as follows.
Add the mustard powder, vinegar and garlic to the yolk, and mix it all in with a whisk. Add a tiny drop of olive oil and whisk that in until it's well blended. Add another bit of olive oil and whisk it in again. Keep doing this until you've added about 2 tbsp oil (after the first couple of drops, you can start adding slightly larger amounts at a time). Taste it, and adjust the flavour if wanted. Keep whisking and adding a dab more oil until it reaches a slightly gelatinous mayonnaisey consistency.
When the asparagus is almost ready, put the toaster down and let it warm the bread up for another 20 seconds or so. Then slice the toast in halves, and arrange each plate with toast and asparagus, sprinkling the cheese over the asparagus and then adding a blob-or-drizzle of mayonnaise over.