Cook the pasta. Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.

Crisp the bacon. In a large skillet over medium heat, cook chopped bacon until crisp. Transfer to a paper towel–lined plate. Leave 1–2 teaspoons of bacon fat in the pan for flavor.

Season and sear the chicken. Pat chicken dry, season with salt, pepper, and 1 tablespoon ranch seasoning. Add a drizzle of oil to the skillet if needed. Sear over medium-high heat until cooked through and lightly browned, about 6–8 minutes. Transfer to a bowl.

Sauté garlic and optional veggies. Lower heat to medium. Add garlic to the pan; cook 30 seconds. If using broccoli, add it now with a splash of water, cover, and steam 2–3 minutes. For spinach or peas, add later with the sauce.

Make the creamy base. In a bowl, whisk Greek yogurt, milk, remaining ranch seasoning, and Parmesan until smooth. Taste and adjust salt and ranch to your liking.

Combine pasta and sauce gently. Add drained pasta to the skillet with the chicken (and spinach/peas if using). Reduce heat to low. Pour in the yogurt-ranch mixture and toss gently. Add splashes of reserved pasta water until the sauce turns glossy and clings to the noodles.

Add bacon and finish. Stir in most of the bacon, saving some for topping. Add red pepper flakes if you like heat. Warm through for 1–2 minutes on low—do not boil, or the yogurt may separate.

Garnish and serve. Top with remaining bacon, extra Parmesan, and chopped parsley or chives. Crack fresh black pepper over the top and serve hot.