Before starting, gather all your ingredients and equipment. Have three plates ready - one for the cooked vegetables, one for the seared meat, and one lined with paper towels for draining.
Heat oil in a large pot over medium heat. Add your quartered potatoes and carrot cubes, cooking them until they're lightly browned on all sides. This takes about 3-4 minutes. Remove them to your paper-towel-lined plate to drain.
Using the same pot, quickly cook your red and green bell peppers for just 30 seconds until they slightly blister. Remove these to your veggie plate.
Turn up the heat to medium-high. Pat your beef cubes dry with paper towels. Add them to the pot in a single layer - don't crowd them. Let them cook for 2-3 minutes on each side until they're nicely browned. Move the browned beef to a clean plate.
Lower the heat back to medium. Add your chopped onions and garlic to the pot. Cook them until they're soft and smell good, about 3 minutes. Put the beef back in the pot and add the fish sauce. Let this cook together for 1-2 minutes.
Pour in your crushed tomatoes, water, and tomato paste. Stir everything well. Once it starts bubbling, turn the heat down to low, cover the pot, and let it cook quietly for about 1½ to 2 hours. Check it occasionally - if the sauce looks too thick, add a little water.
When the meat is tender enough to cut with a fork, add your potatoes and carrots back to the pot. Let them cook for 4-5 minutes. Finally, add your bell peppers and cook for just 1 minute more.
Taste the sauce and add salt and pepper if needed. Let everything rest for 5 minutes before serving with hot rice.
Remember: Your beef should reach 165°F inside to be safe to eat, and it's even better the next day!