Boil a large pot of salted water and add the macaroni. Cook until al dente, about 7-8 minutes, then drain and set aside.
Season chicken breasts with salt and pepper, then cook in a heated saucepan with olive oil over medium heat until done, about 5-7 minutes per side. Remove from pan and slice.
Melt butter in the same saucepan, whisking in flour to form a roux. Gradually add milk, stirring constantly until thick. Remove from heat and add cheeses, mixing until smooth.
Preheat oven to 350°F (175°C). In a baking dish, mix pasta, chicken, and cheese sauce. Bake for 20 minutes until bubbling and golden.
Notes
For storage, keep any leftovers in an airtight container in the fridge for up to three days.