1. Saute bacon just until crisp in a large frying pan; drain on paper toweling, then crumble. Drain off all drippings, then measure 2 tablespoons and return to pan.
2. Halve chicken livers; snip out any veiny parts or skin with scissors. Shake livers with flour and seasoned salt in a paper bag to coat.
3. Brown slowly in drippings in frying pan; stir in mushrooms and liquid. Heat, stirring constantly, to boiling; cover. Simmer 3 minutes, or just until livers lose their pink color.
4. While livers cook, place tomato slices and bun halves in a single layer on rack in broiler pan. Broil 3 to 4 minutes, or until tomatoes are heated through and buns are toasted.
5. Place 2 tomato slices on each bun half; spoon hot liver mixture over, dividing evenly. Top each with another tomato slice; sprinkle with crumbled bacon. Garnish with parsley, if you wish.