To a blender add tomatoes, jalapeno, chicken broth, garlic and salt. Puree until smooth.
In a large skillet, heat oil over medium-high heat. Add onion, and cook until soft.
Pour in the tomato mixture. Bring to a boil and cook for about 10 minutes, stirring occasionally, until it starts to thicken.
Add chicken, stirring to coat and heat for 1-2 minutes until warmed through.
Spread out the tortilla chips in a casserole dish or oven safe skillet. Pour tomato sauce mixture over the chips, making sure to cover them pretty evenly.
Top with cheese. Bake for 10 minutes, or until cheese is melted.
Serve topped with sliced avocado and other optional toppings.