Season the oxtails with salt and pepper.Add oil to large pot and heat over medium heat until hot. Add half of the oxtails to the pot and cook until browned on all sides, about 3-4 minutes per side. Remove the seared oxtails and repeat with the remaining oxtails.
When all the oxtails are browned, add the onion, celery and carrots to the pot and sauté until softened. Add the garlic, green onion and ginger the pan and sauté about a minute stirring often. Add the tomato paste a stir well. Sprinkle flour over vegetable and stir to combine well. Cook stirring for 2 minutes. Add the beer and turn up heat to medium-high. Bring beer/vegetables to a boil and cook for 5 minutes.
Add allspice, stock and oxtails to pot and stir to incorporate. Return pot to a boil and place lid on pot. Once pot is in a full steady boil, lower heat to a simmer. cook oxtails until tender, about 2 hours.