Macaroni and Shrimp Bake

3 cups dried short-cut macaroni
1 tbsp olive oil
6 tbsp butter,
2 small fennel bulbs, thinly sliced and fronds reserved
6 ounces mushrooms, thinly sliced
6 ounces peeled, cooked shrimp pinch of cayenne pepper
1 1/4 cups Bechamel sauce
2/3 cup freshly grated Parmesan cheese
2 large tomatoes, sliced
1 tsp dried oregano salt and pepper

Bring a saucepan of salted water to a boil, add the pasta and oil and cook until tender, but stil firm to the bite. Drain and return to the pan, add 2 tbsp of butter, cover, shake the pan, keep warm.
Melt the remaining butter in a pan. Saute the fennel for 3-4 minutes.Stir in the mushrooms and cook for 2 minutes. Stir in the shrimp, then remove the pan from the heat.
Stir the pasta, cayenne pepper and shrimp mixture into the bechamel sauce. Pour into a greased ovenproof dish. Sprinkle with the Parmesan cheese and arrange the tomato slices around the edge.
Brush the tomatoes with olive oil and sprinkle the oregano on top.
Bake in a preheated oven at 350 F for 25 minutes, until golden brown. Serve immediately.

Bechamel Sauce:
Melt 2 tbsp butter, stir in 1/4 cup flour. Cook, stirring for 2 minutes.
Gradually, stir in 1 1/4 cups warm milk. Add 2 tbsp finely chopped onion, 5 white peppercorns, and 2 parsley sprigs, and season with salt, dried thyme and grated nutmeg. Simmer, stirring for 15 minutes. Strain before using.