Poach fish in water in a medium-size skillet until fish turns from translucent to opaque, 7 or 8 minutes depending upon thickness; remove to a bowl.
Cover with white wine; set aside.
Cook pasta in boiling water in a large saucepan until tender but firm. Drain. Keep warm.
Steam broccoli, mushrooms and bell pepper until crisp-tender 3 or 4 minutes.
Mix Marinara Sauce with buttermilk in a small saucepan; cook over low heat until hot.
Arrange pasta on a large platter. Cover with vegetables. Drain fish and divide into very small pieces and arrange over vegetables. Cover with sauce and cheese, if desired. Lightly toss and serve.