Place chicken in a 4–6 qt slow cooker.
Sprinkle half of the ranch mix and half of the taco seasoning over the chicken. Flip the chicken and sprinkle with the remaining ranch and taco seasonings.
Layer the sliced onion and bell peppers over the chicken.
Add the chicken bouillon cubes and pour in 1 c water.
Cover and cook on low for 6 hours or high for 4 hours, until chicken is fork-tender. Stir occasionally.
With two forks, shred the chicken directly in the slow cooker, mixing it into the sauce.
Serve hot with tortillas and desired toppings.