Add the diced chicken to the pot, season with salt and black pepper, and cook for about 2 minutes until browned.
Add the onion, carrot, red, yellow, and orange bell peppers to the pot. Season with a bit more salt and cook for 5-7 minutes, stirring occasionally.
Add the garlic, stewed tomatoes, paprika, sumac, turmeric, and red chili if using. Stir to combine.
Pressure cook high pressure for 10 minutes. Open the lid once the pressure is fully released, add the zucchini and cilantro, and stir. Serve the chicken ghallaba with rice.