Heat the vegetable oil in a large pot over medium heat. Add the pork cubes and cook until lightly browned on all sides, about 5 minutes. Remove the pork and set it aside.
In the same pot, add the onion, garlic, and ginger. Cook for 2 minutes until the onion softens.
Stir in the Thai red curry paste and cook for 1 minute to release the flavors.
Pour in the coconut milk and chicken broth. Add the fish sauce and brown sugar. Stir well to combine.
Return the pork cubes to the pot. Bring the mixture to a simmer, then cover and cook on low heat for 25 minutes.
Add the sliced bell peppers and continue simmering uncovered for 10 more minutes until the peppers are tender but still hold their shape.
Stir in the lime juice. Taste and adjust seasoning if needed. Serve hot, topped with chopped cilantro.