In a mixing bowl add hung curd, gram flour, ginger garlic paste, salt, pepper, garam masala, and oil. Whisk well. Refrigerate this marinade for 15 minutes. Discard the mushroom stalks and peel the button mushrooms. Heat oil in a non-stick grilling pan. Remove the marinade from the refrigerator. Halve the bamboo sticks. Hold two mushrooms such that their under sides face each other. Coat in the marinade and thread the mushrooms on the bamboo sticks. Grill the mushrooms and apply some marinade on the mushrooms while they are cooking. Grill until a golden brown colour is visible. For the salad, mix julienned tomato, sliced onion, salt, pepper, chaat masala, and lemon juice well. In the serving dish, place the salad in the centre and the mushroom tikka skewers around it. Garnish the salad with a coriander sprig chaat masala and lemon juice. Serve hot mushroom tikkas with a small bowl of mint chutney.