I would not recommend using the microwave for two reasons:
- It does not scale up well as you add mass to the cooking chamber
- The shape and size of asparagus is almost designed to fit into the fact that microwave ovens tend to cook unevenly
Instead, if you wish to cook a large amount of asparagus in a reasonably short period of time, I recommend roasting. The method is very forgiving, but an approach similar to this will give you good results:
- Preheat your oven to approximately 400 F / 200 C.
- Clean and trim your asparagus.
- Please the asparagus in a shallow layer on a sheet pan, and season with salt, pepper, herbs, olive oil, and/or lemon juice as you desire.
- Roast approximately 10-15 minutes until it is slightly browned, and cooked through to your liking
While this technique does not cook a small amount of asaparagus terribly quickly, it does not get any slower for larger batches, and so is probably your most effective method.
Also, many people consider the outcome especially delicious, more so than steaming or microwaving.