Place all the curry ingredients into a food processor/blender (except the meat). Blend until the ingredients turn into a smooth paste and a fragrant scent is released. Taste test the sauce to see if the seasoning is to your liking. If too sour, add more brown sugar; if not salty enough, add more fish sauce; if not spicy enough, add more chili, etc.
Season all sides of the beef with salt and pepper. Make sure to season aggressively because the beef has a large surface area, so you need more seasoning to create a solid foundation of flavor.
Take a medium sized pot (or a pot just large enough to fit the beef) and put it over high heat. Put around ¼ cup of olive oil in the pot, and wait until you can see smoke from the oil. That means the oil is hot enough to start searing the beef. Put the beef in the pan, and sear on all sides (around 1 minute on each side).
Once your beef is seared, pour in the curry paste. If the paste does not cover the beef, add water until the beef is covered. Turn the heat down to low and simmer for 1 hour, or until the beef is tender. You’ll know when the beef is tender when you can pull it apart with a fork with ease.
Once the beef is tender, take the beef out and shred the beef with 2 forks. Pull the beef apart to create these strands of beef, which is going to create a great texture to your beef. Once the beef is done, place back into the pot and simmer until your curry thickens a bit and darkens in color (around 30 minutes). This lets the meat and curry flavors really intensify and develop.
Saute the peppers and onions in a pan over medium - low heat with ¼ cup of olive oil. Season with salt and pepper. The peppers and onions will be done when the onions are a translucent color, around 20 minutes.
Take your flour tortillas (use however many you want to eat) and put them in a dry pan over medium heat. Flip them after 1 minute so that they heat up and get a bit of color on them. Take them off the heat.