Cook pasta according to package directions.
Drain and stir in onion, cucumber and red pepper.
While pasta is cooking, prepare the salad dressing so it has time to cool before adding it to pasta.
In a medium saucepan, cook sugar and vinegar over medium heat until sugar dissolves. Let cool completely.
Then add oil, mustard, salt, garlic powder and parsley.
Pour cooled salad dressing over the pasta mixture.
Stir in tomatoes and olives. Chill overnight.