Set your Instant Pot to sauté mode and heat the vegetable oil. Add the chicken pieces and cook for 3-4 minutes until lightly browned on all sides. Remove chicken and set aside.
Add the diced onion to the pot and sauté for 3-4 minutes until softened and translucent.
Stir in the garlic and ginger, cooking for about 1 minute until fragrant.
Add the curry powder, cumin, turmeric, and cayenne pepper (if using). Stir constantly for 30 seconds to toast the spices.
Pour in the diced tomatoes, coconut milk, chicken broth, and salt. Stir well, scraping up any browned bits from the bottom of the pot. Return the chicken to the pot.
Cancel sauté mode, lock the lid, and set the valve to sealing. Cook on high pressure for 8 minutes.
Quick release the pressure. If using spinach, stir it in now and let it wilt for 2-3 minutes.
Taste and adjust seasoning if needed. Serve over fluffy basmati rice and garnish with fresh cilantro. Enjoy with naan bread if you're feeling fancy!