Prep. Preheat the oven to 400°F and line a baking sheet with parchment paper.
Pound the chicken. Place a chicken breast between two pieces of plastic wrap on a cutting board and pound with a rolling pin to even thickness (about ¼ inch). Repeat with the remaining breasts.
Season the chicken. Season the chicken pieces on both sides with salt, pepper, and garlic powder. Set aside.
Saute the aromatics. Heat the olive oil over medium-high heat in a skillet. Add the shallot and saute until translucent. Add the garlic and saute until fragrant. Turn off the heat and set aside.
Grate the zucchini. Grate the zucchini and then squeeze as much water out of it as possible. You can use your hands or a cheesecloth.
Put it all together. Combine the sauteed aromatics, zucchini, cream cheese, parmesan, salt, pepper, and Italian seasoning in a mixing bowl. Whisk until combined.
Stuff the chicken breasts. Spread about 2 tablespoons of the filling on half of each chicken breast. Top with basil and tomato slices. You’ll want ~2 slices of tomato per chicken piece. Fold the other side of each chicken breast over the filling and secure with toothpicks.
Bake. Arrange the stuffed chicken breasts on the prepared baking sheet and bake for 25 minutes or until the chicken reaches an internal temperature of 165°F.
Rest. Allow the chicken breasts to rest for 5 minutes or so before serving.