In a large saucepan of boiling salted water cook penne until al dente. Drain.
Meanwhile, in a large frying pan over medium-high heat, melt butter and add onion and garlic. Cook for 2 minutes.
Add chopped chicken and continue cooking, stirring occasionally until golden brown, about 5 to 6 minutes.
Reduce heat to medium- low. Drain and chop artichoke hearts and add to frying pan along with chopped tomato, feta cheese, fresh parsley, lemon juice, dried oregano and penne. Cook until heated through, about 2 to 3 minutes.
Season with salt and ground black pepper. Serve warm.