Whisk oil, lemon juice, mustard, garlic, and lemon peel in small bowl to blend. Season dressing with salt and pepper.
Cook penne in large pot of boiling salted water until tender, but still firm to bite. Drain. Rinse pasta with cold water to cool quickly, and drain again. Transfer pasta to large bowl. Add tomatoes, bell peppers, feta cheese, and green onions. Pour dressing over and toss to coat. Season to taste with salt and pepper.