Your full reference would be structured like this:

Author. (Year). Lecture title [Format]. URL of website.

If you are citing a lecture that you got from Blackboard, here is an example (note the URL):

Frank, B. (2015). Lecture 4: Psychophysiology [PowerPoint slides]. Ohio University, Basics of Psychophysiology. Blackboard: http://blackboard.ohio.edu

For APA help, look to the 7th edition Style Manual or the APA Style Blog.