Place chicken in slow cooker (I put them in frozen). Spread pesto on top of chicken. Squeeze juice of 1/2 of a lemon over pesto. Put sliced pats of butter evenly on top. Sprinkle with salt and pepper to taste.
Put on lid and cook on high for 2 hours or on low for 3 to 4 hours. Once done shred with two forks.
In a sauce pan or pot, cook pasta according to package directions to al dente. Drain pasta and pour into slow cooker. Add in cheeses and stir to distribute. Let cook until cheeses are melted. About 5 minutes.
Garnish with parsley if desired and serve immediately.