In a large frypan over medium heat, cook mushrooms and capsicum in 2 tablespoons butter until tender. Remove from heat and set aside.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain. Steam broccoli in colander over pasta water or in steamer until bright green, 5 to 10 minutes.
Toss cooked pasta with 65g butter, Parmesan, oregano, parsley, garlic powder and black pepper. Cover and set aside to keep warm.
In a medium saucepan over medium heat, melt 125g butter. Dump in flour all at once and whisk until smooth. Whisk in cream and chicken stock a little at a time and cook until mixture thickens. Stir in clams and reserved broccoli, mushrooms and capsicum. Heat through and toss with pasta. Serve at once.