Fill a medium saucepan ¾ full of water and add a pinch of salt. Bring to a boil and add snap peas. Boil 1 minute, then drain in a colander and run cold water over until room temperature. Dry thoroughly and dice or use kitchen shears to cut into ¾” pieces.
In a large mixing bowl, combine red onion, salami and cheese.
Add snap peas, olive oil, vinegar, oregano and pinches of salt and pepper. Stir everything together to incorporate, then taste and adjust seasonings to your liking.
Cover and chill at least two hours and up to overnight. Top with pistachios before serving. Leftovers will keep tightly sealed in the fridge up to three days, but note that you may have to drain excess liquid.