In a small dry skillet over medium heat, toast the coriander and cumin seeds, shaking the pan occasionally, until fragrant and lightly browned, about 1:30 to 2 minutes.
Transfer the toasted seeds to a mortar or spice grinder, and grind to a fine powder; transfer to a large bowl.
To the bowl, add yogurt, ghee, lemon juice, ginger, garlic, garam masala, smoked paprika, turmeric and cayenne pepper; set aside.
In the jar of a blender, add papaya chunks and beef broth. Place the lid on and process into a smooth purée.
Add papaya purée to the spice mixture and stir until blended; set aside.
Generously season the beef cubes with salt and pepper. Add the meat to the papaya-spice mixture and stir to coat, pushing the meat down if necessary. Cover and chill for 18 to 24 hours.
KEBABS
The day after, remove the bowl from the fridge and bring the meat to room temperature.
About 30 minutes later, thread on a piece of red pepper followed by a piece of red onion before adding a beef cube, leaving a little gap between each ingredient so the kebabs cook evenly. Repeat the same order, finishing with a piece of red pepper.
Preheat BBQ to 500ºF to 550ºF and using tongs, pour canola oil on a paper towel to grease the grates.
Place the skewers on the grill, close the lid and cook for 12 minutes, rotating every 3 to 4 minutes, or until the internal temperature reaches 145ºF.
Serve kebabs immediately with yogurt and naan bread.