Step 1: In your slow cooker, combine the diced tomatoes (undrained), roasted red peppers (drained and roughly chopped), harissa paste, minced garlic, dried oregano, smoked paprika, cumin, and a pinch of salt and black pepper. Whisk everything together until well combined.
Step 2: Add the boneless, skinless chicken thighs to the slow cooker, nestling them into the sauce mixture. Ensure the chicken is mostly submerged, turning to coat evenly.
Step 3: Cover the slow cooker and cook on LOW for 6-7 hours or on HIGH for 3-4 hours, or until the chicken is fork-tender and easily shreds. The exact cooking time may vary depending on your appliance.
Step 4: Once the chicken is cooked, carefully remove the chicken thighs from the slow cooker and place them on a cutting board. Using two forks, shred the chicken into bite-sized pieces. Set aside.
Step 5: Add the softened cream cheese and heavy cream to the sauce remaining in the slow cooker. Whisk vigorously until the cream cheese is fully melted and the sauce is smooth and creamy. Taste and adjust seasoning if needed.
Step 6: Return the shredded chicken to the slow cooker and stir to combine, ensuring all the chicken is coated in the luxurious creamy harissa sauce.
Step 7: Serve immediately, garnished with fresh cilantro or parsley, if desired.