正确的方式进行异步调用

I have a situation where scalability is of utmost importance. I have an API endpoint which has to make a call to a 3rd party web service and it could take over 10 seconds to complete. What I'm concerned about is web requests stacking up on our server while waiting for the 3rd party requests to complete. I need to make sure that the requests to "StartJob" return immediately and the job actually runs in the background. What's the best way to do this?I have a situation where scalability is of utmo