Preheat the oven to 230°C.
Place the pancetta slices on a baking rack set in a sheet pan and roast for 8 to 10 minutes until crisp. Remove from the oven and set aside to cool.
Meanwhile, bring 2 to 3 litres of water to a boil in a large pot and add 1 tablespoon of salt. Fill a large bowl with ice water and have a sieve or colander ready in the sink.
Put the snap peas into the boiling water for only 10 or 15 seconds, drain, and put immediately into the ice water. Cool completely and drain. Cut each snap pea in half lengthwise and place in a large bowl.
Place the snap peas in a large bowl and add the red onion.
To make the vinaigrette, whisk together the olive oil, vinegar and lemon juice. Pour enough vinaigrette on the snap peas to moisten. Crumble the pancetta over the salad and add 1 teaspoon salt and the pepper. Add the Parmesan and toss well.