Cut chicken breasts in half lengthwise or pound until they are ½ inch thick. Season on both sides with salt and pepper.
Add ¼ cup flour to a shallow bowl. Dredge chicken in flour and transfer to a sheet tray.
Heat 1 tablespoon oil in large cast iron skillet over medium high heat. Add chicken and cook until golden brown and fully cooked through, 5 minutes per side. Remove to a plate and set aside. Wipe out skillet.
In same skillet, reduce heat to medium and add remaining 1 tablespoon oil. Add onions and cook until soft and translucent, 5 minutes. Add garlic and cook until fragrant, 1 minute. Add remaining 2 tablespoons of flour and incorporate with a wooden spoon. Start with just a small drizzle, slowly incorporate chicken broth, mixing between additions.
Once all the broth is added, mix in pesto and milk. Add tomatoes. Bring sauce to a simmer and cook until thickened, 5 minutes. Reduce heat to low and add chicken back in. Cook until warmed through, 2 minutes. Garnish with fresh basil and serve immediately.
Video
Notes
Storage: Store any leftovers in an airtight container. They will last about 3-4 days in the fridge.Freezing Instructions: You can freeze the chicken with the sauce for up to 3 months. To re-heat, thaw in the fridge overnight and warm on the stove or in the microwave until heated through.Substitutes: For best results, follow the recipe as is. However here are some common substitutes that would work well in this recipe.
Instead of all-purpose flour, you can use almond flour or other grain-free flours.
Instead of milk, you can use almond milk or cream cheese for a thicker sauce.
Instead of chicken broth, you can use more milk or vegetable broth.
* Please note the nutrition label does not include the pasta.