In a large pot with 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. Add artichoke hearts, tomato, feta cheese, fresh parsley, lemon juice, dried oregano and drained penne to the large frying pan. Toss and cook until heated through, about 2 to 3 minutes.