Prep chicken: Pat chicken pieces dry and season lightly with salt and pepper.
Sauté aromatics (optional): In a skillet, heat oil and sauté onions, garlic, and ginger for 2–3 minutes until fragrant. This step enhances the flavor but can be skipped for convenience.
Combine ingredients in slow cooker: Add chicken, sautéed onion mixture (or raw), coconut milk, diced tomatoes, curry powder, cumin, coriander, turmeric, chili powder, salt, pepper, sugar/honey, and optional vegetables. Stir to combine.
Slow cook: Cover and cook on low for 4–5 hours or high for 2–3 hours until chicken is tender and cooked through.
Adjust consistency and seasonings: If the curry is too thick, add a little water or chicken broth. Taste and adjust salt, spice, or sugar as needed.
Serve: Garnish with fresh cilantro and serve hot with steamed rice or naan bread.