Preheat grill pan or indoor electric grill to high.
Combine yogurt, curry paste, lemon juice, and cilantro in a shallow dish. Add chunks of chicken and coat evenly in yogurt sauce. Lace meat onto metal skewers. When you are about 10 minutes away from eating, place chicken on hot grill and cook 5 or 6 minutes on each side, until charred at edges and chicken meat is firm.
Place a small heavy skillet on stovetop over high heat. When pan is very hot, add whole tomatoes. Pan roast the tomatoes until charred on all sides. Place the tomato sauce and charred fresh tomatoes in a food processor. Return skillet to heat and toast mustard and coriander seeds and crushed red pepper until they pop. Add seeds and flakes to food processor with a few pinches coarse salt. Pulse grind tomato mixture into a chunky chutney and transfer to a small bowl. When you remove chicken from grill, add flat bread to blister and warm it through. Slide chicken off skewers on to a serving dish. Set bowl of tomato chutney with a serving spoon along side. Pile chicken into or onto flat bread with tomato chutney to top. Potatoes with cumin are a perfect side to this meal.
Serving suggestion: Potatoes with Cumin, recipe follows.
Boil potatoes in salted water to cover until tender, about for 7 minutes. Drain potatoes, return to hot pot to dry them out.
Heat skillet over medium high to high heat. Add cumin seeds. When seeds pop and crackle, add oil, then onion. Saute onion 2 minutes, stirring constantly. Add potatoes to the pan and toss to coat and lightly brown, about 3 minutes. Remove the pan from heat, season with salt, to taste, and serve.