In a skillet set over medium-high heat, add the oil. When it's hot, add the ginger and onions and cook until softened and beginning to turn golden, about 3 minutes. Add the curry leaves, garam masala, mustard seeds and cardamom seeds, and cook for 20 seconds. Add the ground beef, sprinkle with salt and stir to break up any chunks. Continue to cook until the beef is cooked through, about 8 minutes. Stir in the peas and cook until they turn bright green, about 2 minutes. Place a stovetop steamer over medium-high heat and bring to a boil. Add the cabbage leaves and steam until bright green and tender, 2 to 3 minutes. Place them on a platter and spoon the beef on top. Garnish with green chilies and lemon wedges.