This is a dish I make on a regular basis.
Firstly I cook the gluten free pasta according to the instructions on the box.
In a separate pan I cook off the onion, peppers, and mushrooms. I prefer to have cooked onion in the salad, but of course you could just add raw diced onions and pepper. Sometimes I add pancetta to the salad. Once cooked I let it cool. I usually do this by removing it from the pan and placing it on a cold plate.
Separately I dice some cucumber and place this in a bowl.
Once the pasta is cooked I drain and then rinse the pasta in cold water to stop it cooking and cool it down.
I then combine the ingredients and dress the salad with salt, pepper, olive oil, and white wine vinegar.
The only downside I have found, is that the gluten free pasta generally doesn’t last, and goes somewhat chewy and tough if you leave it until the next day. I certainly didn’t have this issue when I made pasta salads using wheat based pasta.