PREHEAT oven to 425°F.
COMBINE 1 cup flour, cornmeal, undissolved yeast and salt in a large bowl. Add very warm water and oil; mix until well blended, about 1 minute. Gradually add enough remaining flour to make a soft dough. Dough should form a ball and will be slightly sticky. Knead** on a floured surface, adding additional flour if necessary, until smooth and elastic, about 4 minutes. Cover and let rest on floured surface while preparing toppings. (If using RapidRise Yeast, let dough rest at this point for at least 10 minutes.)
COMBINE chicken, process cheese, diced tomatoes and chiles, 1 cup crushed tortilla chips and 1/3 cup salsa in a medium mixing bowl.
ROLL dough into 12-inch circle; place in greased pizza pan; sprinkle with additional cornmeal, if desired. OR, pat dough with floured hands, pressing gently to fill greased pizza pan or baking sheet. Form a rim by pinching the edge of the dough; prick surface with fork.
SPREAD chicken mixture evenly over crust. Bake on lowest oven rack 12 to 15 minutes until center is set and crust is golden brown.
TOP with remaining chips and salsa, lettuce and sour cream.
*If you don't have a thermometer, water should feel very warm to the touch.
**To knead the dough, add just enough flour to the dough and your hands to keep the dough from sticking. Flatten dough and fold it toward you. Using the heels of your hands, push the dough away with a rolling motion. Rotate dough a quarter turn and repeat the "fold, push and turn" steps. Keep kneading dough until it is smooth and elastic. Use a little more flour if dough becomes too sticky, always working the flour into the ball of dough.