Cook the pasta in salted boiling water for 2 minutes less than the package directions. Drain and place in a buttered 9x13 baking dish. Set aside.
In a large saute pan melt the butter and the oil. Add the onions, mushrooms, red pepper, thyme, salt, and pepper. Cook until the onions become translucent and the mushrooms become soft. About 6-7 minutes. Sprinkle the flour over the mix and stir until combined. Cook for 1 minute. Whisk in the chicken stock and milk. Turn heat to low and continue cooking until the sauce begins to thicken.
Remove the pan from the heat and stir the tuna, cheese and the peas. Pour this mixture over the pasta and combine well.
In a small bowl combine the bread crumbs, cheese, pepper, and the butter. The bread crumbs should be moist. Sprinkle the crumbs over the casserole and place it in a 350-degree oven for 30-40 minutes or until the topping is browned. Let sit 10 minutes before serving.