Preheat the oven to 400°F (200°C) and place the tortilla on a baking sheet or pizza stone. Bake for 3-4 minutes until slightly crisp. Remove from the oven and spread 2 tablespoons of ranch dressing over the tortilla, then sprinkle with chopped basil and shredded mozzarella. Add the chopped chicken and tomatoes on top. Return the tortilla pizza to the oven and bake for another 6-8 minutes, or until the cheese is bubbly and the edges are golden brown. Let it cool for a minute before slicing and serving.