In a large frypan over medium heat cook red, yellow and green capsicums in 2 tablespoons olive oil with garlic until just tender. Stir in diced tomatoes, reduce heat to medium-low and simmer 10 minutes. Remove to a serving bowl.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
While pasta is cooking, heat 2 tablespoons oil and butter over medium heat in a large frypan. Cook chicken in butter mixture until juices run clear, 5 to 10 minutes. Mix cooked chicken with tomato sauce and sprinkle with basil, rosemary, thyme, garlic powder and Parmesan. Serve over cooked pasta.