Preheat oven to 375°.
Cooking spray an 8x8 pan or deep dish pie plate.
Cook pasta according to package direction, drain and place in a large bowl.
Cut up 2 1/2 strips of the bacon and add to the bowl.
Add the peas and tuna to the bowl.
Heat oil and butter in a large sauce pot and melt the butter.
Add onion and sauté 3 minutes.
Reduce heat to medium. Sprinkle flour over onion mixture, stirring until blended; cook, stirring constantly, 2 minutes.
Gradually stir in milk, whisking.
Bring to a simmer; stir in cheddar cheese, and seasoning.
Cook 1 minute or just until cheese melts.
Pour over the ingredients in the bowl, stirring to mix.
Pour mixture into 11x7 inch pan (I used my mega 3 inch deep pie plate).
Cut up the remaining 2 1/2 strips of bacon and mix with the cup of breadcrumbs.
Spread evenly over the casserole.
Bake uncovered, at 375°, for 1 hour. **