Preheat the oven to 375 degrees F (190 degrees C).
Cook bacon in a large skillet and over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon on paper towels and cool.
Pour oil into a 12-inch cast iron skillet. Brush oil all over the interior of the skillet. Place dough into the skillet and shape into a pizza, forming a crust at the edge. Prick dough all over with a fork.
Bake in the preheated oven for 5 minutes. Remove from oven and reshape dough if necessary. Sprinkle the top of the dough with 2 teaspoons ranch seasoning. Spread ranch dressing on top.
Sprinkle shredded mozzarella, chicken, and red onion over pizza crust. Crumble cooled bacon on top.
Bake in the preheated oven until cheese is melted and top is browned, about 20 minutes.
Remove pizza from oven and top with tomato slices. Melt butter and mix in the remaining dry ranch seasoning. Brush crust with butter-ranch mixture.
Set an oven rack about 6 inches from the heat source and preheat the oven's broiler.
Broil pizza until cheese is golden brown, 2 to 3 minutes, being careful not to burn.