To blanch the peas, bring a large pot of well-salted water to a boil. Prepare a large bowl of well-salted ice water and set it nearby.
Add the peas to the boiling water, let the water return to a boil, then cook for 2 more minutes. Remove the peas from the boiling water and immediately plunge them into the ice water. When the peas are cold, drain them and lay on paper towels to dry.
Cut the peas in half lengthwise, then set aside.
Coat a medium saute pan with olive oil, then add the garlic and red pepper flakes. Set the pan over medium heat and cook for 2 to 3 minutes. Remove the garlic with a slotted spoon and set aside.
Add the prosciutto and cook for 3 to 4 minutes, or until crispy. Add the red wine vinegar. Turn off the heat.
In a large bowl, combine the arugula, snap peas, onion and garlic.
Scatter the crispy prosciutto on top and any juices from the pan.