Remove the tops from the peppers and reserve. With a small, sharp knife, remove the white membrane and seeds from inside the peppers, taking care not to tear the flesh.
Mix together the mashed potatoes, provolone, Parmigiano, egg, chives, garlic, salt and pepper.
Using a small teaspoon, fill the peppers three-quarters full with the mixture; the stuffing will puff up and if too full will ooze out the top. Put the tops back in place. Pack the peppers tightly into an ovenproof dish (use a nice one so you can serve in the same dish), drizzle with olive oil and bake for about 30 minutes, until tender.