Chapotraphouse

Most things can just be washed, because dangerous bacteria is only present in trapped soil on the surface. Some things need to be examined and have damaged parts/layers removed, like with green onions. Some things can never actually be definitively safe, like lettuce, because they harbor the bacteria inside their leaves (this is why lettuce is the #1 cause of food poisoning by overall numbers, even if there are more dangerous individual foods like oysters).

Then there's pickling and fermenting, which usually makes things much better anyways and which kill off undesirable bacteria by creating a highly acidic environment. For example, raw cabbage isn't great and cooked cabbage is revolting, but cabbage pickled alongside strong aromatics like garlic, onion, and ginger is fantastic.

Wash with water like normal, cut up, and then put in water with a sterilizing solution. They are very common in countries with known unsafe tap water. Some might be labeled "vegetable wash", make sure it disinfects.

The other helpful replier covered this, but you can handle things like lettuce by doing the above strategy: disinfect after cutting into the pieces you will use. For example, it is common in Mexico to cut up some cabbage, put what you will use in a bowl of water, and add some disinfectant.