Place the chicken breasts in the bottom of the slow cooker. Add the onion mixture. Add the tomatoes with green chilies, diced tomatoes, and chicken broth. Stir to combine. Cook on low for 3-4 hours until the chicken is cooked through.
To make baked tortilla strips. Preheat the oven to 400 degrees. Place the tortillas in a stack. Cut them in half and then into ½ inch strips. Spray a baking sheet with cooking spray. Place the strips on a baking sheet in a single layer. Spray the tops with cooking spray. Sprinkle with salt. Bake for 5 minutes. Shake the pan and bake for 5 more minutes or until golden brown.