Blend garlic, ginger, vinegar, paprika, cayenne, cumin, coriander, mustard, cinnamon and salt into a smooth paste, scraping the blender as needed.
Heat oil in a skillet over medium heat and cook onion for 8 minutes. Stir in the spice paste for 2 minutes, keeping the heat moderate so it does not scorch.
Add tomato sauce and broth, scrape the bottom and pour into a 5-quart slow cooker. Fold in chicken and potato pieces.
Cover and cook on low for 5 to 6 hours until chicken reaches 165°F and potatoes are tender through their centers.
Stir gently, keeping the chicken chunks intact, and skim excess surface fat. Divide among 6 bowls with the thick red sauce coating both chicken and potatoes.