Heat the olive oil in a heavy based pot and sweat your onion until it has softened. About 5 minutes.
Blanch the peas in boiling water for 3 minutes, remove and refresh under cold water. Set aside.
Add the rice and stir to coat the grains. As they just start popping / catching add the white wine and stir continuously until it is absorbed.
Add the garlic and continue stirring and the hot stock one ladle at a time until the risotto is cooked but still al dente. Stir almost continuously
About 3 minutes before the end, add the gammon, parsley, zest and peas.
Stir in the grated Parmesan, and adjust seasoning to your taste.