Lotus pureus
Neither asparagus nor a pea but it does have pods which are eaten like a 'mangetout' pea and does have a taste reminiscent of asparagus! Easy to grow producing numerous winged pods which should be picked at about 2.5cm (1in) long and steamed or sauted whole.
Asparagus Pea Seeds from Mr Fothergill's Seeds and Plants. 35 seeds. Crisp asparagus-flavoured pods.