In a large pot of boiling salted water, cook pasta according to package instructions; drain well.
Season shrimp with salt and pepper, to taste; set aside.
Melt 2 tablespoons butter in a large skillet over medium high heat. Add garlic, oregano and red pepper flakes, and cook, stirring frequently, until fragrant, about 1-2 minutes.
Add shrimp and cook, stirring occasionally, until pink, about 2-3 minutes; set aside.
Melt remaining 6 tablespoons butter in the skillet. Stir in pasta, arugula and Parmesan until arugula begins to wilt, about 2 minutes. Stir in shrimp.
Serve immediately, garnished with parsley, if desired.