Heat olive oil in a large skillet over medium high heat. Add garlic and onion, and sauté until onions become translucent, about 2-3 minutes.
Stir in coconut milk, tomato paste, flour, ginger, curry powder, garam masala, chili powder, and salt & pepper until well combined and slightly thickened, about 1-2 minute.
Place chicken into a slow cooker. Cover with sauce mixture. Cover and cook on low heat for 6 hours, or high heat for 3 hours.