If i eat two healthy small meals for lunch and breakfast, can i have anything for dinner and not put on weight?

i normally have bran flakes for breakfast, then a salad with maybe half a baked potato for lunch, or a sandwich made with whole meal bread! i also exercise everyday normally for about 45minutes. can i have whatever for my dinner, obviously nothing too calorific, still moderately healthy!and not put on weight? i also have a little bit of chocolate nearly everyday, is that bad?