If using raw chicken, heat a drizzle of olive oil in a large skillet over medium heat. Cook the chicken through, about 6 to 8 minutes, then shred or dice. For rotisserie chicken, remove the skin and shred the meat evenly. Set aside.

In the same skillet over medium heat, sauté the diced onion for 3 to 4 minutes until softened and translucent. Add the minced garlic and cook for 1 more minute until fragrant. Add the shredded chicken back to the pan and stir to combine.

Push the chicken mixture to one side of the skillet. Add the butter to the open space and let it melt. Pour in the heavy cream and bring to a gentle simmer. Gradually stir in the grated Parmesan a little at a time, stirring constantly to prevent lumps. Add the Italian herbs, salt, pepper, and red pepper flakes if using. If the sauce is too thick, add a splash of cream. If too thin, simmer 1 more minute.

Fold the chicken mixture gently into the alfredo sauce until evenly coated. If adding spinach or mushrooms, stir them in now and cook 1 to 2 minutes until just wilted. Avoid overmixing to keep the chicken from turning mushy.

Spoon the creamy Chicken Alfredo Sloppy Joes mixture generously onto toasted buns. Serve immediately while hot.