Place chicken thighs and onion in the crockpot. Whisk the remaining ingredients for the chicken and pour over the chicken and onions. Stir to coat fully.
Cook on high for 4-6 hours. Once cooked, remove chicken and shred using two forks.
Meanwhile, blend the ingredients for the sauce until thick and smooth.
Assemble tacos with chicken, sauce, and taco ingredients of your choice!