Prepare the slow cooker by lightly coating the insert with cooking spray or a small amount of oil.
Place the chicken breasts in the bottom of the slow cooker. Season with garlic powder, onion powder, dried parsley, salt, and pepper. Place the mushrooms and cream cheese around the seasoned chicken.
In a small bowl, whisk together the cream of chicken soup, cream of mushroom soup, and chicken broth. Pour over chicken.
Cover and cook on low for 4 to 5 hours, or until the chicken is cooked through and tender.
Remove the chicken from the slow cooker and shred it with two forks. Return the shredded chicken to the slow cooker.
While the chicken is removed, stir in the mozzarella, and parmesan until melted and smooth.
Return the chicken to the crockpot, along with the frozen peas. Stir to combine.
Cover and cook for an additional 15 minutes.
While the peas are cooking, prepare the pasta as directed on the package and toast the panko. In a small skillet, toast the panko over medium heat. Remove from heat and set aside.
To serve, spoon the chicken tetrazzini over pasta and top with toasted panko and fresh parsley before serving.