1.In a large pot of boiling water, cook rotelli until just tender but still firm, about 8-10 mins. Drain well and keep warm.
2. Meanwhile, in a saute pan, heat olive oil. Add onion and garlic, cook until softened, 2-3 mins. Add shrimp and cook, until pink 2-3 mins longer.
3. Add olives, oyster sauce, and lemon juice. Reduce heat and cook 2 minutes to slightly reduce. Add the feta, oregano and pepper. Cook until cheese melts about 1 min.