Prepare the ingredients as listed above so everything is ready to use.

Mix the mayonnaise, ketchup, and mustard in a small bowl to make the sauce. Set aside.

Heat the vegetable oil in a skillet over medium heat. Add the diced onions and sauté for 5–7 minutes until golden and caramelized. Remove from heat.

Divide the ground beef into two patties per portion and shape into patties slightly larger than the buns. Season with salt and black pepper.

Heat a grill pan or skillet over medium-high heat. Cook the patties for 2–3 minutes on the first side, then flip and cook to your desired doneness. Top each patty with a slice of American cheese and allow it to melt.

Toast the hamburger buns cut-side down in the skillet until golden.

Assemble the burgers: Spread sauce onto the bottom bun, then layer with romaine lettuce, tomato slices, the cooked patty with melted cheese, and caramelized onions. Place the top bun on.

Make the mango lassi: Blend the mango, yogurt, milk, cardamom, and sugar together until smooth. Adjust sweetness to taste.

Serve the burgers with carrots, hummus, and mango lassi.