Place cast iron skillet over fire 2-3 minutes before cooking to preheat.
First, add some canola oil and butter. Once butter has melted, add garlic, lemon juice, beer, salt and pepper. Stir and let simmer for 1 minute. Finally, add mussels and top with green onions. Let simmer until all the shells have fully opened (about 10-15 minutes).
Pull skillet of charcoals, garnish with parsley, and enjoy!