Bring 1½ gallons of water plus 1 tablespoon of salt to boil in a large pot. Add the crabs and cook for 20 minutes. Remove the crabs (saving the cooking liquid) and give them an ice bath.
Clean the crabs of their meat, saving all the bones (I'm guessing he means shells because crabs are invertebrates and do not have bones) and innards but discard the lungs. Mix the crab meat with the green onions and set aside.
In a low, wide pot, add 3 tablespoons of canola oil and saute onion, Guajillo chiles, garlic, thyme, black pepper, salt, tomatoes, bones (I think he means shells) and innards from the crab, for ten minutes at high heat. Add the cooking liquid from the crab and bring to a low boil. Cook for 15 minutes.
Puree everything in a blender or food processor and strain through a medium strainer. (I'm not sure I would puree the shells but I will try to find out.)
To serve, pour the soup into bowls and add crab meat with the green onions. Top with cilantro (optional), and serve with Tequila (optional of course).