Heat your 1 tbsp olive oil over medium heat and add your bacon. Fry until crisp then drain and set aside. Return your pan to the heat and add your butter. Once the foaming has subsided, add your flour. Gradually add your milk, whisking frequently, until all incorporated. Add your chicken stock. Bring to a boil then reduce to a simmer and cook for 15 minutes or so, or until thick and glossy.
Add your peas and stir to heat through. Add salt, pepper, nutmeg, pasta, cooked bacon and stir through to combine.
Add all of your cheeses. Stir through pasta and remove from the heat.
Mix together your breadcrumbs, herbs, butter and the 1/2 cup parmesan. Sprinkle over your mac and cheese and grill until golden and bubbling.