For the marinade, whisk together the yogurt, garlic, ginger, garam masala, coriander, turmeric, cumin, 1 tablespoon of the lime juice, and 1 1/2 teaspoons of the salt in a large ziplock bag. Make two or three cuts into the top of each chicken thigh and add the thighs to the marinade. Turn them to coat them well and gently massage the marinade into the cuts. Seal the bag and refrigerate the chicken overnight.
Take the chicken out of the refrigerator 30 minutes before cooking. Heat your grill or grill pan to medium-high. While the pan heats up, use a paper towel to wipe any excess marinade off the chicken, brush the onion slices with the canola oil, and liberally oil the grates. Grill the chicken and onions, turning them once, until the onions are tender and charred, about 3 minutes, and the meat is just cooked through, about 6 minutes.
While the chicken and onions are cooking, combine the mango chutney, mayonnaise, and remaining teaspoon of lime juice in a small dish.
Transfer the chicken and onions to a cutting board and sprinkle the onions with the remaining salt. Tent the chicken with foil and let it rest for 5 minutes. Slice the chicken across the grain into 1/2-inch strips. Warm the tortillas under a damp paper towel in the microwave for 50 seconds. Spoon 2 teaspoons of the chutney sauce down the center of each tortilla, then top them with the chicken and onions, adding a few sprigs of cilantro, if desired. Roll the tortillas burrito-style, then cut each in half on the diagonal.