Dont want to make you jealous, but I am having asparagus for the third time this week .. mine have been in the ground for just over three years now. They were put in as crowns .. 9 of them. They really are a hit and miss plant with just 2 ouf the 9 producing lots of spears.
The asparagus bed is only active for 5 or six weeks a year, so there is no reason for not slotting in a few things like lettuece and spring onions. The spring onions I would strt off in a 2" x 2" module. Put about 10 or 12 seeds in a few modules and then transplant when they are about 3" tall. Have done this for a few years now and have great results. Start more of in 4 weeks time and keep them coming.