Heat the vegetable oil in a large pot over medium heat.
Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and grated ginger, cooking for an additional 1-2 minutes until fragrant.
Add the ground cumin, ground coriander, turmeric, and cayenne pepper to the pot. Stir well and cook for another minute to toast the spices.
Add the chicken pieces to the pot, browning them on all sides for about 5-7 minutes.
Pour in the coconut milk and chicken broth, then stir in the tomato paste and lemon juice. Season with salt and pepper to taste. Bring the mixture to a gentle simmer.
Cover the pot and let it simmer for 30-40 minutes, or until the chicken is cooked through and tender.
If using boneless chicken, reduce the cooking time to about 20-25 minutes.
Once cooked, remove the chicken from the pot and let it rest for a few minutes before serving.
If desired, you can thicken the sauce by simmering it uncovered for an additional 10 minutes.
Serve the chicken curry over rice or with flatbread, garnished with fresh cilantro.