Grease a 9 x 12-inch baking pan, and preheat oven to 350 degrees. Brown and drain 1 to 1 1/2 pounds hamburger. Add to this 1 taco seasoning packet and 8 to 12 ounces plain tomato sauce. Snip 2 tubes of Pillsbury biscuits into fourths and drop evenly into pan. Top with meat mixture and spread evenly over biscuits. Sprinkle 8 to 12 ounces of shredded mozzarella cheese over meat. Bake at 350 degrees for about 25 minutes or until biscuits are done in middle. Immediately cover with shredded lettuce; then add 1/2 chopped onion and 1 tomato chopped. Drizzle taco sauce over and top with 2 handfuls of crushed Doritos.