In a large pot, heat the oil on medium-high. Season the chicken with salt and pepper. Add to pot and cook 5–7 min., until golden brown, stirring occasionally.
To pot, add the simmer sauce. Drain any excess liquid from the spinach, cauliflower, and peppers and stir into sauce. Heat to a boil on high. Reduce heat to simmer and cook 5 min., stirring occasionally. Season with salt to taste.
Meanwhile, heat the rice according to package directions. Serve tikka masala over rice and garnish with the cilantro.