In a slow cooker, combine the diced onion, minced garlic, Italian seasoning, salt, black pepper, and crushed red pepper flakes (if using).

Pour in the chicken stock and stir everything together.

Add the chicken breasts to the slow cooker.

Sprinkle the chopped sundried tomatoes over the top.

Cover and cook on low for 6-8 hours or on high for 3-4 hours until the chicken is cooked through and tender.

Remove the chicken breasts from the slow cooker and shred them using two forks. Return the shredded chicken to the slow cooker.

In a separate bowl, whisk together the heavy cream and cornstarch until smooth. Pour this mixture into the slow cooker and stir well to combine.

Cover and continue cooking on high for an additional 30 minutes.

Meanwhile, cook the lasagna noodles according to package instructions. Drain and set aside.

Stir in the fresh spinach until wilted.

Just before serving, add the cooked lasagna noodles to the slow cooker and stir gently to incorporate.