1. Preheat oven to 375°. Cook pasta according to package directions, omitting salt and fat; drain.
2. Heat oil and butter in a Dutch oven over medium-high heat until butter melts. Add onion; sauté 3 minutes. Reduce heat to medium. Sprinkle flour over onion mixture, stirring until blended; cook, stirring constantly, 2 minutes. Gradually stir in milk. Bring to a simmer; stir in cheddar cheese, salt, and pepper. Cook 1 minute or just until cheese melts. Stir in peas and tuna.
3. Add pasta, tossing to coat. Pour pasta mixture into an 11 x 7-inch glass or ceramic baking dish coated with cooking spray. Sprinkle with panko and Parmesan cheese.
4. Bake at 375° for 20 minutes or until bubbly and golden.