Preheat the oven to 350 degrees F (175 degrees C). Spray a large baking pan with olive oil cooking spray.
Heat oil in a large skillet over medium heat. Add tomatoes, onion, garlic, and jalapeno peppers, then stir in chicken broth, taco sauce, flour, cumin, oregano, chili powder, and salt. Cook until heated through, 5 to 10 minutes. Add shredded chicken, mixing vigorously until ingredients are well blended; cook until hot, 2 to 3 minutes.
Wrap 8 tortillas in damp paper towels and microwave on high until soft and flexible, about 30 seconds. Repeat twice more to heat remaining tortillas.
Spoon about 2 tablespoons chicken mixture down the center of a tortilla and sprinkle with Cheddar cheese. Roll tightly around the filling and place seam-side down in the prepared baking dish. Repeat to form remaining taquitos. Spray taquitos with cooking spray and sprinkle with remaining Cheddar cheese.
Bake in the preheated oven until cheese is melted and taquitos are crispy, 20 to 22 minutes.
Place shredded lettuce on a serving platter and arrange taquitos on top. Serve with sour cream and guacamole.