Place chicken breasts in a shallow dish or resealable bag and pour in the Italian dressing to coat; marinate in the refrigerator for 1 hour or up to overnight.
Remove chicken from the marinade and discard excess dressing. Pat the breasts dry with paper towels.
Grill over medium heat or pan-sear in a lightly oiled skillet until cooked through, about 12–14 minutes total, turning once, until internal temperature reaches 165°F (74°C).
Preheat the oven broiler and position a rack about 6 inches from the heat source. Line a rimmed baking sheet with foil if desired.
Place the cooked chicken breasts on the baking sheet. Spread about 2 tablespoons of pizza sauce on top of each breast.
Top each sauced breast with your chosen pizza toppings, then sprinkle evenly with shredded mozzarella.
Broil the chicken just until the cheese is melted and bubbly, watching closely so it does not burn, about 2–4 minutes.
Remove from the oven and let rest a couple of minutes before serving.
