Bring a pot of water to a boil. Add a splash of olive oil and a pinch of salt, and cook the pasta until al dente – not too soft.
Drain and rinse with cold water. Add the remaining olive oil and toss to coat. Set aside for the moment
Preheat oven to 375 degrees F. Use a little butter to grease a large casserole dish.
In a large pot or Dutch oven, melt the 3 tablespoons butter over a medium setting. Allow the butter to cook for about 30 seconds, but not brown. Add the flour, whisking constantly, and allow it to cook for about a minute. Again, avoid browning it, and adjust heat if necessary.
Add about a half a cup of the milk, stirring constantly, till it thickens. Be sure to scrape from the bottom and sides as you continue to stir.
When the sauce is evenly mixed, add the rest of the milk slowly as you stir.
Cook for about 5 minutes, stirring frequently, until it is bubbling and thick.
Turn the heat to medium low, and add about two-thirds of all three cheeses, stirring until melted.
Add the rosemary, thyme, salt, pepper, and lemon zest.
Now, add the macaroni and peas, and stir to coat evenly.
Pour the macaroni into the prepared casserole dish.
Top with remaining cheeses.
Bake in the oven 30 to 35 minutes. The casserole should be golden brown on top.