Heat a large non-stick frying pan over medium heat. Brush the chicken with oil, salt and pepper. Cook for 4 minutes each side or until cooked through. Allow to cool and slice. Heat a char-grill pan over low heat. Use an 8cm-round cookie cutter to cut rounds from each slice of bread. Brush with the butter and char-grill for 2 minutes each side or until golden and crispy. Spread over the mayonnaise and horseradish and top with the chicken, spinach and radish to serve. Makes 12.