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

1. 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.
2. 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.
3. 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.
4. Bake in a preheated oven at 350 F for 25 minutes, until golden brown. Serve immediately.
5. 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.