Prepare the pasta according to package directions.
While the pasta is cooking, heat the oil over medium-high heat in a large skillet and saute the onion until tender and translucent, about 5 minutes.
Add the garlic and cook for another minute.
Add the chicken and cook until no longer pink.
Add the diced tomato and cook for another minute.
Add the half-and-half/flour mixture, pesto and salt and stir to combine.
Bring to a boil, reduce the heat to low, cover, and simmer for 5 minutes, stirring occasionally.
Drain the pasta and add it to the skillet. Toss in the sauce to coat.
Add the fresh basil leaves and toss to combine.
Serve immediately with some freshly ground black pepper and grated Parmesan cheese.
