Preheat oven to 400F. Spray a 9x13 baking dish with cooking spray and set aside.
Heat olive oil over medium heat in a medium skillet.
Add chicken and cook 3-4 minutes per side, or until cooked through. Remove cooked chicken to a bowl or stand mixer and shred. (If using ground chicken, this will take less time, just use a spatula to break up as it browns and cooks.)
Return chicken to the skillet and stir in taco seasoning, tomatoes and jalapenos. Stir and simmer for about 5 minutes.
Meanwhile, place your beans in a bowl, add the cumin, garlic, and salt. Stir to combine, then use a fork to roughly mash the beans. I leave then somewhat chunky, but not completely whole.
Place the taco shells in the baking dish, standing up. You may have to do a line of taco shells and then a couple on the side to fit 10.
Place a spoonful of the beans in the bottom of each shell and gently spread across so that the bottom is covered. Top with the chicken mixture, leaving about 1/3 of the shell "open" for toppings.
Cover the tops with cheese (lots of glorious cheese!)
Bake, uncovered, for 12-14 minutes or until cheese is fully melted and the edges of the shells are browned.
Remove from the oven and fill with your favorite toppings!