MAKE THE BBQ SAUCE:
Heat vegetable oil over MED heat in a saucepan and add onions and garlic. Saute for about 5 minutes, until soft and translucent.
Add remaining ingredients, stir, reduce heat and simmer for about 10 minutes.
Transfer sauce to a blender or food processor and process until smooth.
Strain sauce through a fine mesh sieve, by pushing on it with a rubber spatula or back of a spoon. Scoop the solids from the sieve, place in small bowl and set aside.
BAKE THE CHICKEN:
Preheat oven to 450 degrees F. Spray a baking dish with cooking spray and place chicken breasts in the dish. Sprinkle with salt and pepper. Spread reserved bbq sauce solids over the chicken, and then pour about 3 tablespoons of the strained bbq sauce over the chicken. Turn to coat completely in sauce. Bake chicken for about 15-18 minutes, until fully cooked and juices run clear.
Remove chicken to a bowl and let sit for 10 minutes. Using two forks, shred chicken and set aside.
MAKE THE CREAMY BBQ CHEESE SAUCE:
To a mixing bowl, add creamy bbq cheese sauce ingredients, except cheese, and whisk to combine. Stir in cheese. Mix about half the sauce with the shredded chicken, and set remaining sauce aside.
ASSEMBLE THE NACHOS:
Preheat oven to 375 degrees F. Spray a baking dish or cast iron pan with cooking spray, then add tortilla chips. Spoon creamy bbq cheese sauce over the chips, then top with shredded chicken. Sprinkle with chopped red onions, then sprinkle with Mexican cheese and Mozzarella cheese. Drizzle strained bbq sauce over the top of the cheese.
Bake for about 5-10 minutes, or until cheese is melted and slightly bubbly.
Add desired toppings and enjoy!