In a 5- to 6-quart slow cooker, whisk together the tomatoes, tomato paste, ginger, curry powder, ½ teaspoon salt and ¼ teaspoon pepper.
Add the chicken, cauliflower, onion and raisins to the slow cooker and stir to combine. Cook, covered, until the chicken is cooked through, 4 to 5 hours on high or 6 to 7 hours on low.
Twenty minutes before serving, cook the rice according to the package directions. Spoon the chicken mixture over the rice and top with the cilantro. Serve with yogurt and lemon wedges, if desired.