The designs must be heavily influenced by sustainability and all materials used must be either renewable, reusable, or recyclable.
The competition is open to individuals or teams of up to five people, one of whom must be a resident of London.
The first round of judging will pick the winning 14 designs, and teams will be allocated a parking bay to be transformed overnight on 3 July.
The second round will see the 14 parking bays judged in situ on 4 July. There will be three awards, for best use of recycled materials, most innovative use of space, and most sustainable intervention.
The judges are: former RIBA president George Ferguson; Peter Murray, director of the London Festival of Architecture 2008; Mark Whitby, chairman, Rambøll Whitbybird; Kevin Carmody of Carmody Groake; Ruth Slavid, The Architects' Journal; Paul Priestman of Priestman Goode; and Ken Yeang of Llewellyn Davies Yeang.
The deadline for submissions is Monday 9 June.