Preheat oven to 350°F. Prepare a casserole dish by lightly greasing with oil or butter. Set aside.Get frozen peas out to thaw. In a large saucepan over medium-high heat, add the pancetta and cook for 5 minutes.
Then reduce heat to medium and add diced onions, cover, and cook for another 5 minutes, or until onions are soft.
Then add chopped garlic and cook for 1 minute while stirring, so garlic doesn't burn. Remove from heat and set aside. Pour pasta into casserole dish and then add the pancetta/onion mixture and the thawed peas. Pour the Béchamel on top of the pasta and mix well to combine.
Top with the parmesan and small cubes of butter.
Cover with tinfoil and bake for 20 minutes, or keep warm in oven until ready to serve.Once removed from oven, let dish stand for 5 minutes, then serve warm. When serving, this dish tastes great with a little fresh lemon juice squeezed on top.
Enjoy!!