To the bottom of a 6 quart slow cooker, add the Harissa paste and 1 Tbsp of the olive oil. Add onion, potatoes, carrots and 1/2 tsp salt and stir gently to combine.
In a small bowl, add garlic powder, smoked paprika, pepper and remaining 1/2 tsp salt. Stir, and sprinkle evenly over chicken thighs.
Add remaining 1 Tbsp olive oil to a large skillet and heat over MED-HIGH. Add chicken thighs, skin side down, and cook 4-5 minutes, until golden brown.
Place browned chicken thighs over the top of vegetables in slow cooker. For extra harissa flavor, spoon some paste over the chicken and spread to cover. Cover and cook on LOW for 8 hours.
Serve chicken thighs with vegetables and a spoonful of cooking juices spooned over the top. Garnish with parsley and a squeeze of fresh lemon juice.