Bring a large pot of salted water to the boil, and then cook 1 pound of pasta according to package directions. About four minutes before the pasta is done, add some broccoli florets to the hot water. While the pasta cooks, you can cook the chicken and make the miso sauce.
Cut two boneless, skinless chicken breasts into 1-inch pieces then season with salt and freshly ground black pepper.
Add olive oil to a large skillet over medium-high heat. Then, add the chicken until cooked through and browned on all sides.
Remove the chicken from the pan and turn the heat to low. Add butter to the pan, once the butter melts add the miso. Stir the butter and miso until combined. Now, remove the pan from the heat completely.
Add the Greek yogurt and stir to combine.
When done, drain the pasta and broccoli, reserving 1/4 cup of the pasta cooking water. Then, add the pasta, broccoli and reserved water to the sauce.
Now, add some shredded Parmigiano-Reggiano cheese.
Add the chicken then use tongs or two large spoons to toss the pasta.
Serve the pasta with a handful of finely sliced green onions sprinkled on top.