In large pot, boil spaghetti according to package directions.
While pasta is cooking, in cast iron (or heavy skillet) pan, heat olive oil on medium and add garlic for about 30 seconds.
Toss in rapini and cook for about 4-5 minutes, or until slightly tender.
If pasta sticks to pan, add about 1/4 cup of pasta liquid and continue to toss. You can also use a little white wine, or a bit of both.
Transfer to serving platter and toss with more Parmigiano cheese.
Serve immediately!