To a large mixing bowl, add all the ingredients mentioned under marinade except lemon juice. Mix well.
Taste test and add more salt and lemon juice. If the marinade tastes sour, skip lemon juice.
Add the mushrooms, bell peppers and onions. Mix well.
If using wooden skewers, rinse them under running water.
Preheat air fryer or oven to 200 C or 400 F for atleast 15 mins. If using stovetop, heat a non-stick griddle with 1 tablespoon oil.
Thread the veggies on to skewers - onion, bell pepper & mushrooms.
Place the skewers on a prepared baking tray. Place them in the oven or air fryer or on a griddle.
Oven - Grill them for 10 mins & then brush the skewers lightly with some marinade. Turn the skewers to the other side and brush if needed. Grill them again for 6 to 7 mins depending on the size of the mushrooms.
Air fryer - Air fry for 8 mins, then brush them with little marinade. Turn the skewers to the other side and repeat brushing lightly. Air fry again for 5 mins. Adjust the timings based on the size of mushrooms.
Stove top - Place the skewers and keep turning them to all the sides and cook on a high heat. Some of the marinade comes to the griddle, you can use a wooden spatula to bring it together. When the veggies wilt, place a wired rack on the stovetop and place the mushroom skewers over direct flame and grill until done.
To char the tandoori mushrooms, brush some butter or mustard oil and place the skewers back in the oven. Broil or air fry for another 2 mins.
When done perfectly, grilled mushroom tikka & onions will begin to smell so good. Brush with more butter or oil if needed and serve immediately.