Cut chicken crosswise into strips; season with half each of the salt and pepper.
In large skillet, heat 1 tbsp of the oil over medium-high heat; sauté chicken until golden, about 3 minutes. Transfer to plate.
Add tomatoes, onion, garlic, oregano and remaining oil, salt and pepper
to skillet; sauté for 2 minutes. Add radicchio; sauté until tomatoes
begin to split and soften, about 2 minutes. Return chicken to skillet;
add green onions and heat through.
Meanwhile, in large pot of boiling salted water, cook linguine until
tender but firm, about 10 minutes. Drain and return to pot; add sauce
and toss to coat.
Serve sprinkled with Parmesan cheese.