Gather your ingredients: slice the onion, mince the garlic, grate the ginger, and cut the chicken into bite-sized pieces.
In a mixing bowl, combine the garlic, ginger, garam masala, turmeric, and cumin to create your spice blend.
Add the sliced onions, chicken pieces, and spice mixture to the slow cooker, layering them evenly.
Pour the coconut milk over the ingredients, ensuring everything is coated and submerged.
Cover the slow cooker and cook on LOW for 6 to 8 hours, or on HIGH for 3 to 4 hours, until the chicken is tender and the sauce is fragrant and slightly thickened.
Once cooked, check the sauce; it should be glossy and cling to the chicken. Taste and add salt or a squeeze of lemon for brightness if desired.
Garnish with toasted nuts and chopped cilantro for added texture and flavor. Serve hot over rice or with naan bread.