Preheat your oven to 375°F (190°C). Cook the bacon until crispy, then crumble and set aside. In a bowl, mix cheddar cheese, cream cheese, mayonnaise, crumbled bacon, and ranch seasoning until well combined. Slice a pocket into each chicken breast, being careful not to cut all the way through. Stuff the cheese and bacon mixture into each chicken breast and secure with toothpicks if needed. Season the chicken with salt and pepper. Heat olive oil in a skillet over medium-high heat and sear the chicken breasts on each side for 2 to 3 minutes until golden brown. Transfer to a baking dish and bake for 20 to 25 minutes or until the internal temperature reaches 165°F (74°C). Let the chicken rest for 5 minutes before serving. Garnish with parsley if desired.