Cook the penne pasta in a large pot of salted boiling water according to package directions until al dente. Just before draining, reserve 1 cup of the pasta water, then drain the pasta.

While the pasta cooks, add the chopped bacon to a large skillet or Dutch oven over medium-high heat. Cook until crispy, about 6-8 minutes. Use a slotted spoon to transfer the bacon to a paper towel-lined plate, leaving about 1 tablespoon of grease in the skillet.

Add the cubed chicken to the skillet. Season with salt and pepper and cook until golden brown and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.

Add the chopped onion to the skillet and cook for 2-3 minutes until it begins to soften. Add the minced garlic and cook for another minute until fragrant.

Reduce the heat to low. Pour in the chicken broth and add the dry ranch seasoning. Add the softened cream cheese and whisk until it melts completely and the sauce is smooth.

Gradually stir in the shredded cheddar and mozzarella cheese until fully melted. If the sauce is too thick, add a splash of the reserved pasta water to thin it out.

Return the cooked chicken and three-quarters of the crispy bacon to the sauce. Add the drained penne and stir until everything is well-coated.

Serve immediately, garnished with the remaining bacon and fresh green onions.