Procedures

Soak the kidney beans overnight. Add the soaked kidney beans along with water in a pressure cooker and cook for 1 whistle. Allow it to cool down and then drain the water. Add the kidney beans to a strainer and allow it to sit for sometime till the residual water has drained away. Mash the kidney beans and keep aside.
Heat 1Tsp olive oil in a fry pan. Add the green chillies, cumin powder, onions and fry for 2mins till the onions become translucent. Add the garlic and fry for 1min more. Add the mushrooms, oregano, salt, red chilly powder and cook for another 2min on high flame. Turn off the flame and allow it to cool.
Add the onion and mushroom mixture along with coriander to the mashed kidney beans and mix well. Adjust salt and chilly powder if required as per taste.
Make large balls from the mixture and press each between the palms for desired patty thickness. Usually for charcoal grilling 1/2″ thickness is desired.
Brush patty with little olive oil before putting on the grill.
Add the patty to the charcoal grill and allow cooking for 10min each side turning them once. Wrap the sliced veggies except lettuce for dressing in an aluminum foil and cook them in charcoal grill for 5min.
When the patty is almost done add the burger buns with cut side on the grill and heat for 2min. Allow the patty to cool for 2min so that the juices rearrange inside uniformly.
Arrange the burger as desired with lettuce, cheese slice, mustard sauce and serve with a side of French fries if desired.
Note:
The kidney beans should not have water else the patty will not hold during grilling
Kidney beans can also be substituted with black beans.