In a large mixing bowl, whisk together the yogurt, tomato paste, garlic, ginger, lime juice, garam masālā, paprika, salt, turmeric, red chili, and black salt. Adjust seasoning to taste. The mixture should be pungent, spicy, and salty.
Add the tofu, onion, and bell pepper to the mixing bowl and stir gently until each piece is well coated. Transfer to an airtight container and refrigerate overnight, or up to 24 hours.
When ready to cook, preheat the oven to 450°F (230°C). Remove the mixture from the refrigerator and stir, then skewer onto 4 to 6 stainless-steel or bamboo skewers. If using bamboo skewers, they must first be soaked in water for 1 hour. Alternate the tofu, pepper, and onion on the skewers. Reserve any remaining marinade.
Line the bottom of a 9 x 9 x 2-inch (23 x 23 x 5 cm) square baking dish with foil (for easier cleanup). Balance the skewers on top of the baking dish rims so the tofu is touching neither the bottom of thepannor its neighbor.
Bake the tofu skewers for 15 minutes, until starting to brown in spots. Remove from the oven, brush with the remaining marinade, rotate each skewer 180 degrees, then return to the oven for an additional 10 minutes, until browning in spots again. If desired, broil for a minute or two to obtain a char reminiscent of tandoor cooking.
Remove from the oven and sprinkle with chāt masālā to taste and chopped cilantro. Serve hot with lemon wedges and rāitā if desired.