Heat the olive oil in a cast-iron skillet or heavy-bottomed pan over medium-high heat.
Season the chicken thighs with salt and black pepper. Place them in the hot skillet skin-side down and sear until the skin is golden brown.
Remove the chicken from the skillet and arrange it skin-side up in the crock pot.
In a medium bowl, combine the ketchup, soy sauce, honey, minced garlic, onion powder, dried thyme, dried parsley, and dried mustard. Whisk until smooth and well combined.
Pour the prepared sauce evenly over the chicken thighs.
Cover the crock pot and cook on HIGH for about 3 hours or LOW for about 5 hours, until the chicken is fully cooked and reaches an internal temperature of 165°F (74°C).
Transfer the Crock Pot Chicken Thighs to a serving dish. Spoon the warm honey garlic sauce from the crock pot over the chicken and garnish with fresh chopped parsley before serving.