Heat olive oil in nonstick pan and quickly sear chicken thighs on each side. Transfer chicken thighs to slow cooker. Add butter and onions to pan and cook just until they start to soften, 3-5 minutes. Then transfer onions and butter to slow cooker.
Add cream of chicken soup, chicken broth, and seasonings to slow cooker and stir to combine. Cover and cook on high for 3 hours. After 3 hours, remove chicken thighs and shred. Return shredded chicken to slow cooker and add frozen mixed vegetables and cook for another hour on high.
Preheat oven to 375°. Place biscuit dough on top of chicken and vegetable mixture. Using oven mits, transfer just the CrockPot ceramic insert to oven and bake for 15-20 minutes or until biscuits are cooked through. Brush biscuits with mixture of melted butter and garlic powder and sprinkle with parsley.