1. Prepare pasta according to package directions. Drain & set aside.
2. In a large skillet, heat oil over medium-high. Add onion & mushrooms. Cook 3-5 minutes or until onions are soft, stirring throughout.
3. In a small bowl, add cornstarch & cold milk. Whisk together.
4. Add cornstarch mix, flour & pepper to skillet. Bring to a boil, stirring constantly. Reduce heat to medium. Stir in peas & carrots. Cook 5 minutes.
5. Add tuna & 1/2 cup cheese. Mix well. Stir in pasta & heat until warm.
6. Top with remaining cheese & serve.