In a large skillet, heat butter and olive oil over medium-high heat. Season chicken thighs with salt and pepper. Add chicken to the skillet, skin-side down, and sear both sides until golden brown, about 2-3 minutes per side. Place chicken thighs into a 6-qt slow cooker.
In a large bowl, whisk together pineapple juice, chicken broth, brown sugar, soy sauce, honey, vinegar, Sriracha, garlic and ginger.
Pour pineapple juice mixture over chicken. Top with pineapple chunks, crushed pineapple and reserved juices.
Cover and cook on LOW heat for 5-6 hours or HIGH for 2-3 hours, basting every few hours.
In a small bowl, whisk together 1/4 cup water and cornstarch. Stir in cornstarch mixture, red bell pepper and onion into the slow cooker. Cover and cook on HIGH heat for an additional 30-60 minutes, or until sauce is thickened.
Serve immediately over steamed rice, garnished with sesame seeds and parsley, if desired.