In a small bowl, combine the canola oil, cumin, and kosher salt. Rub the mixture onto the meat. Let it set for about 15 minutes.
In a small bowl, mix the sour cream, milk, Chipotles, and salt.
Heat the grill to medium-high heat. Cook the skirt steak for 6 or until temperature in thickest part reaches 145°, turning once. Cut the steak into strips.
To assemble each torta, spread the beans onto the bottom slices of bread. Spread the sour cream-Chipotle mixture on the top slice of bread.
Fill the tortas with meat, cheese, slices of avocado, onion, and tomato. Serve warm.