In a large dutch oven or large pot, heat oil on medium high heat. Brown meat on all sides. Remove from heat and let rest on a cutting board for about 10-15 minutes.
In a food processor, pulse soy sauce, fish sauce, tomatoes, and garlic until smooth.
Slice the rested beef against the grain into thin slices.
Cover dutch oven and bring stew to simmer on medium high heat. Bring heat down to medium low to low and cook with the lid on for about 1-2 hours or until the meat is tender enough to cut with a fork, but not stringy.
Finish by stirring in the calamansi or lemon juice. Season with salt and pepper to taste.