Cut onion into thin slices and mince garlic cloves.
In a large skillet, warm the olive oil over medium-high heat until hot but not smoking. Add the onion and garlic and cook until the mixture is golden, about 5 minutes.
Add the tomatoes, oregano, basil and pepper, and bring to a boil over medium-high heat , breaking up the tomatoes with a spoon. Reduce the heat to low, cover and simmer, stirring occasionally, while you cook the pasta and prepare the shrimp.
Add the pasta to the boiloing water and cook until al dente 10 to 12 minutes, or according to package directions .
Shell and devein the shrimp.
Uncover the sauce and bring to a boil over medium-high heat. Add the shrimp, reduce the heat to low, cover and simmer for 3 minutes.
Add the olives and half the feta cheese and stir to combine.
Drain the pasta and serve topped with the shrimp and sauce. Garnish each serving with remaining feta cheese.