Heat olive oil in a large skillet over medium-high heat.
Season the chicken thighs with salt and black pepper, then place them skin-side down in the skillet.
Sear the chicken for about 6-8 minutes until the skin is golden brown, then flip and cook for another 3-5 minutes.
Remove chicken from the skillet and set aside on a plate.
Add sliced onion to the skillet and sauté until translucent, about 4 minutes.
Add minced garlic and sauté for another minute until fragrant.
Stir in the sliced apples and cook for 3-4 minutes until slightly softened.
Pour in the apple cider and stir in the Dijon mustard and thyme.
Return the chicken to the skillet, skin-side up, and simmer gently for 25-30 minutes.
Adjust seasoning with salt and pepper before serving.