Pat dry the chicken thighs with paper towels and season with salt and pepper on both sides.
Add the olive oil to a large cast-iron skillet or heavy bottom pan over medium-high heat.
Place the chicken skin side down in the hot pan and sear until golden brown.
Remove the chicken from the pan and place it in a single layer, skin-side up in the crock pot.
Add the ketchup, soy sauce, honey, minced garlic, chopped onion, dried thyme, paprika, and dried mustard to a mixing bowl. Whisk the ingredients together until well blended.
Pour the mixture over the chicken in the slow cooker.
Place the lid on the slow cooker and cook on high for 3 hours or low for 5 hours.
When finished cooking, pour the sauce out of the slow cooker and skim off any excess fat. If needed, heat until thickened.
Remove the chicken from the slow cooker and place on a serving dish. Spoon the sauce over the chicken and garnish with fresh chopped Italian parsley.
Serve with mashed potatoes or rice and your favorite green vegetable.