Boil vinegar in heavy small saucepan over medium heat until reduced by half, about 3 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 pot of boiling salted water until crisp-tender, about 4 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.