The phrase "planned mosque" refers to an intended or proposed mosque building, meaning that someone has made preparations or created a design for a future mosque that will be built. Full definition
Rep. Anthony Weiner, a past and probably future foe of Mayor Michael Bloomberg, is praising the mayor for his stance on the controversial planned mosque near Ground Zero. (blogs.wsj.com)
It is very likely that said planned mosque is being built by Sunnis and the arson was due to Shiites or vice versa. (religion.blogs.cnn.com)
Signs at the construction site for his planned mosque had been vandalized twice and federal investigators had determined that a fire at the site was intentionally set. (religion.blogs.cnn.com)