For an even more colorful spread, replace half the trout with smoked salmon.
Preheat oven to 350°. Cut each bread slice into 4 triangles. Brush with olive oil, and sprinkle with pepper and 1/4 tsp. salt. Place in a single layer on a baking sheet; bake 15 to 20 minutes or until golden.
Stir together sour cream, next 3 ingredients, and remaining 1/4 tsp. salt. Spoon about 1 1/2 tsp. sour cream mixture onto each bread triangle. Top with radish slices and trout.