Rinse the oxtails and pat them dry
Season with salt, black pepper, garlic powder, onion powder, paprika, and thyme
Heat oil in a large pot or Dutch oven
Brown the oxtails on all sides
Remove the oxtails and set aside
Sauté chopped onions, garlic, carrots, and celery in the same pot
Add tomato paste and cook for 1 to 2 minutes
Pour in beef broth or water
Add bay leaves, thyme, and any additional seasoning
Return the oxtails to the pot
Bring to a boil
Reduce to a low simmer
Cover and cook for 2.5 to 4 hours until tender
Stir occasionally and add more liquid if needed
Add potatoes or beans if desired during the last 45 to 60 minutes
Taste and adjust seasoning
Serve hot with rice, mashed potatoes, or bread