The correct way:
You have two metrics: money and technical optimisation (execution time/storage/memory optimisation )
You need to show how much more revenue you brought in by implementing a new feature. Of course the marketing and sales teams would bring in the new clients, but you claim your features did. The second aspect is cost reduction. Say you migrated an app that runs on EC2 to lambda. You can claim cost reduction. You calculate this using the cost to run this server for a day or an year and the same on a lambda. Don't consider other services that might be running on the EC2. Or it will get too complex.
As far as technical optimisation is concerned, you can use profilers to check for execution times of code blocks, memory, storage and show that you reduced some of it by x percent.
Of course, you are going to be asked questions on how you did something. You should be able to answer them.
The incorrect but easier way:
Just put in random numbers. Nobody is gonna check. As long as you can explain what's written, you are good.
Saying something like you reduced the execution time of the x module by y percent. And when asked you say you moved certain parts of the module from a blocking architecture to async once. You used profilers to determine where bottlenecks were and implemented multithreading. This reduced runtime significantly.