Boil vinegar in small saucepan over medium heat until reduced by half, about three minutes.
Pour vinegar into large bowl. Whisk in oil, mustard, marjoram and garlic.
Season dressing to taste with salt and pepper.
Cook asparagus in large pan of boiling salted water until crisp-tender, about four minutes.
Drain; rinse with cold water and drain again.
Add asparagus and bell pepper to dressing; toss to blend well.
Sprinkle with pecans and serve.