Heat olive oil in a skillet over medium-high heat and cook chicken thighs until browned on the outside, about 10 minutes. Transfer to a slow cooker.
Grind garlic granules, chili powder, ground cumin, paprika, pepper, sugar, mustard powder, coriander, oregano, thyme, cayenne, ginger, cumin seeds, and sea salt in a mortar and pestle to make the spice mix.
Sprinkle 1/2 the spice mix over the chicken and pour in enough water to cover. Add remaining spice mix, tomato puree, shallots, onion, red bell pepper, yellow bell pepper, and honey to the slow cooker.
Cover and cook on Low until flavors are well combined and chicken is no longer pink in the center, 6 to 8 hours