Take each chicken breast and cut it evenly down the middle, lengthwise.
Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Pat the chicken breasts dry and season both sides with ½ teaspoon each of salt and ½ teaspoon of pepper.
Once hot, carefully lay the chicken in the pan. Let them sear for 4-5 minutes, then flip and continue cooking for an additional 5 minutes. Remove them from the pan and set aside. Make sure the chicken reaches an internal temperature of 165°F and continue cooking if needed.
Turn the heat down to medium and add the onions and garlic. Cook for 3 minutes to soften the onions, stirring occasionally.
Add the tomato paste and cook for 1-2 minutes, stirring into the onions.
Drizzle in the remaining oil, and sprinkle in the flour. Cook for 1 minute, stirring to combine.
Whisk in the milk, Italian seasoning, garlic powder, and remaining salt and pepper. Continue cooking until thickened, about 2 minutes. Taste and adjust for seasoning, if needed.
Add the chopped tomatoes and return the chicken and any drippings to the pan to warm through.
*I like using chicken breasts because I can cut each one in half lengthwise to make four portions. You can also use 4 boneless, skinless chicken thighs or pork chops, but the cooking time will vary depending on their size and thickness. Cook chicken to an internal temperature of 165°F. Cook pork chops to 145°F, then let them rest for at least 3 minutes.**Whole milk creates the creamiest sauce, but 2% milk also works. You can also use an unsweetened, unflavored dairy-free milk, although the consistency may vary depending on the type you use.***I chose Roma tomatoes because they were the most affordable fresh option at my grocery store! You can also use grape or cherry tomatoes, slicing tomatoes, heirloom tomatoes, or canned diced tomatoes (drained). Aim for about 1½ cups of diced tomatoes.