Preheat oven to 400 F.
Bring a large pot of salted water to a boil, add in your pasta and cook until al dente (see package for timing) Reserve 1 cup of pasta water in case you need to thin out your sauce. Continue steps below while pasta cooks.
In a medium sauce pan heat olive oil over high heat and saute onions until translucent (about 5 minutes) add in minced garlic and cook until fragrant. Add both cans of tuna and cook on medium heat for 2 minutes.
Pour broth into tuna mixture and add frozen peas. Continue to cook at a low simmer until pasta is finished. Strain pasta and transfer to a 9"x 13" casserole dish.
In a small bowl mix together cold water with cornstarch and add to your tuna mixture, allow to simmer for 1 minute and remove from heat.
Stir in the grated parmesan cheese and then pour half of the mixture over your pasta. Stir to mix and then top the pasta with remaining sauce. Sprinkle top with breadcrumbs, fresh pepper and grated cheddar cheese.
Cook in preheated oven for 10 minutes, until the top is brown and cheese is melted.