Bring a large saucepan of lightly salted water to a boil over high heat. Add the angel hair pasta and cook until al dente; 3 to 4 minutes. Drain and keep warm.
Heat the olive oil in a large frypan over medium-high heat. Add the sausage slices and cook until lightly browned on both sides; about 2 minutes per side.
Reduce the heat to medium and stir in 2 tablespoons of butter along with the onion, garlic, capsicum, stir fry vegetables, salt and pepper. Cook and stir until the sausage is no longer pink in the centre and the vegetables have softened; 10-12 minutes.
Meanwhile place the clams, mussels and prawns in a steamer over 2cm of boiling water and cover. Remove the prawns once they turn pink; after about 3 minutes. Remove the clams and mussels as soon as they open; after 3 to 5 minutes all together. Discard any clams and mussels that do not open. Set the seafood aside and keep warm.
Place the scallops into the frypan with the vegetable mixture and gently cook until the scallops are no longer opaque in the centre; about 3 minutes.
Gently stir in the steamed seafood, parsley and remaining 2 tablespoons of butter.
Serve the seafood and vegetable mixture over a bed of angel hair pasta.