In a bowl combine the salad oil, vermouth, lemon juice, salt, oregano, and garlic.
Cut fish into 1-inch pieces; place in the marinade.
Cover and marinate the fish at room temperature for 1 hour.
Drain fish, reserving the marinade.
Cut the green pepper into 1-inch squares.
On 6 skewers, alternate fish, green pepper, and tomatoes; end with the mushroom crowns.
Broil over medium coals 8 to 10 minutes, turning often and basting with the marinade frequently.