In 3-quart saucepan, heat oil over medium-high heat. Cook onion in oil 5 minutes, stirring frequently, until tender. Stir in garlic, tomato paste, pepper flakes and sugar. Cook 1 minute, stirring constantly. Stir in diced and sun-dried tomatoes. Reduce heat to medium-low. Simmer 10 minutes, stirring occasionally, until very thick. Remove from heat; stir in basil, salt and pepper.