In a large pot with boiling salted water cook penne pasta until al dente. Drain.
Meanwhile, in a large skillet over medium-high heat melt butter, add onion and garlic and 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 them, chopped tomato, feta cheese, fresh parsley, lemon juice, dried oregano, and drained penne pasta to the large skillet. Cook until heated through, about 2 to 3 minutes.
Season with salt and ground black pepper. Serve warm.