Cook the pasta. Bring a large pot of salted water to a boil and cook the fettuccine according to the package directions.
Reserve about 1/2 cup of pasta water before draining.
Season the chicken. Pat the chicken dry, then season both sides with garlic powder, Italian seasoning, salt, and black pepper.
Cook the chicken. Heat olive oil in a large skillet over medium heat. Cook the chicken for 5 to 6 minutes per side, or until fully cooked and lightly golden. Remove it from the pan and let it rest for a few minutes before slicing.
Start the sauce. In the same skillet, melt the butter.
Add the minced garlic and cook for about 30 seconds, just until fragrant.
Add the flour. Stir in the flour and cook for 1 minute. This helps create a smooth, slightly thicker sauce without needing heavy cream.
Pour in the milk and broth. Slowly whisk in the almond milk and chicken broth. Keep whisking until the sauce looks smooth and begins to thicken, about 3 to 4 minutes.
Finish the sauce. Lower the heat and stir in the Parmesan cheese and Greek yogurt.
Mix until creamy and fully combined. If the sauce seems too thick, add a splash of reserved pasta water.
Add vegetables if using. Stir in broccoli florets or spinach and cook until tender. Spinach will wilt quickly, while broccoli may need a few extra minutes.
Combine everything. Add the cooked pasta to the skillet and toss it in the sauce.
Top with sliced chicken and a little parsley before serving.