Heat oil in a skillet over medium heat then add potatoes and carrots. Cook the vegetables until they are lightly browned on each side then transfer to a plate with paper towels to drain the oil.
immediately add the bell peppers after and cook for about 30 to 45 seconds. Once they're cooked, include them in the other draining
Drain the oil from the pan but leave two tablespoons worth of oil then increase the heat to medium-high heat. Add beef and cook for about 1 to 2 minutes on each side or until lightly browned then remove it from the pan and let the meat rest.
If the oil reduced, add another teaspoon before adding the onions and garlic to cook.
Once the onions and garlic have softened from cooking, add back the beef then pour the fish sauce and cook for about 1 to 2 minutes.
While the meat and sauce are cooking, add crushed tomatoes, water, and tomato paste. Stir them all together then bring to a boil.
Lower heat, cover, and cook for about 1 1/2 to 2 hours or until beef is tender. If you see the sauce drying out before the meat tenderizes, add more water in 1/2 cup increments.
Add potatoes and carrots to the pot and continue to cook for about 4 to 5 minutes or until vegetables are tender and sauce is thickened and reduced as desired.
Add bell peppers and cook for about 1 minute or until tender yet crisp then season the stew with salt and pepper until it suits you taste.