I applied through university. The process took 1 week. I interviewed at George Mason University
Interview
Submit name and courses you want to teach to the department, and find two professors who are willing to recommend you. People with more teaching experience generally get what they want to teach and those with less experience may not get their desired class.
Interview questions [1]
Question 1
As long as you have good support from the professor, they would give you a summer class to teach.