Chop the small yellow onion.
In a large mixing bowl, carefully whisk together the tomato paste, white vinegar, minced garlic, chili powder, ground ginger, paprika, ground cloves, ground cinnamon, ground cumin, dry mustard and sugar.
Place the chicken breasts and chopped onion in the base of the slow cooker and pour the vindaloo sauce over and around the chicken. Season with pinch of salt and pepper.
Set on low and cook for 8 hours. Once the chicken is cooked, shred with fork and combine with the sauce.
Cook the rice as directed.
Serve Slow Cooker Chicken Vindaloo with rice and veggies.
Instant Pot Instructions: add chicken breasts, onion and alls the seasonings to insert. Close the lid and set to Sealing. Cook on High, Manual for 15 to 18 minutes, or until cooked through. Let pressure release naturally. Keep on warm mode until ready to serve - shred the chicken into the sauce, straining if needed. Serve over rice with veggies.