In a large skillet over medium heat, cook mushrooms and bell pepper 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 1/4 cup butter, Parmesan, oregano, parsley, garlic powder and black pepper. Cover and set aside to keep warm.
In a medium saucepan over medium heat, melt 1/2 cup butter. Dump in flour all at once and whisk until smooth.
Whisk in cream and chicken broth a little at a time and cook until mixture thickens. Stir in clams and reserved broccoli, mushrooms and bell pepper.