I think there's two ways you could take that dish, but both ways you definitely want to add some good quality extra virgin olive oil like GB suggested. The first would be to add a cheese like feta or ricotta salata at the end before you serve it. IMO either cheese pairs better than parm with the roasted tomatoes and grilled chicken. Some finely diced red onion and cucumber would add color, texture, and freshness.
The other way would be to not add any cheese, but to add some lemon juice, capers, some type of olive like gaeta or nicoise, and red onion.
"Boldness has genius, power, and magic in it."
Johann Wolfgang Von Goethe