Place the flour on a plate or in a bag. Cut the chicken breasts in half lengthwise to create thinner pieces. Season both sides with salt and pepper, then coat evenly with flour. For more even pieces, you can pound the chicken between plastic wrap before coating. Wash your hands thoroughly after handling raw chicken.
Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the flour-coated chicken and cook for about 5 minutes on each side until golden brown. Remove the chicken from the skillet and set aside. If necessary, cook in batches and add more oil between batches.
In the same skillet, add the remaining tablespoon of olive oil. Sauté the diced onion over medium-high heat for 2 to 3 minutes until translucent and soft. Add the sliced sun-dried tomatoes and minced garlic and cook for an additional 1 to 2 minutes.
Add the baby spinach and stir just until wilted. Pour in the heavy cream, then add ½ cup of the parmesan cheese along with the Italian seasoning. Season with salt and pepper to taste. Simmer over medium-low heat for 2 minutes until the sauce thickens.
Return the cooked chicken to the skillet and cook on low heat for 2 to 3 minutes until heated through.
Top with fresh basil and serve over your favorite pasta or rice, accompanied by crusty bread if desired.