Place the chicken breasts in a shallow bowl or resealable bag and pour in the Italian dressing to coat. Marinate in the refrigerator at least 1 hour or up to overnight.
Remove chicken from the marinade and pat dry. Grill over medium heat or sear in a skillet until cooked through, about 12–14 minutes total, turning once, until internal temperature reaches 165°F (74°C).
Preheat the oven broiler. Arrange the cooked chicken on a rimmed baking sheet.
Spoon about 2 tablespoons of pizza sauce onto each chicken breast and spread evenly. Top with your chosen pizza toppings.
Sprinkle shredded mozzarella over the toppings. Broil the chicken on the top oven rack until the cheese is melted and bubbly, watching closely to avoid burning, about 2–4 minutes.
Remove from the oven and let rest a few minutes before serving.
Notes
Marinate at least 1 hour for best flavor.
Pat chicken dry before cooking for better browning.
Use a rimmed sheet to catch any drips while broiling.
Watch the broiler closely; cheese can burn quickly.