Mix soy sauce, calamansi or lemon juice, brown sugar, garlic, black pepper, and salt in a bowl.
Add beef to the marinade, ensuring each piece is coated. Transfer to a resealable bag or airtight container.
Marinate beef in the refrigerator for at least 2 hours or overnight.
Heat vegetable oil in a frying pan or skillet over medium-high heat.
Remove beef from marinade, allowing excess liquid to drip off. Reserve marinade.
Fry beef slices for 2-3 minutes per side. Cook in batches if necessary.
Pour reserved marinade into the pan and simmer for 2-3 minutes, stirring occasionally, until slightly thickened.
Serve beef tapa over jasmine rice with a fried egg. Drizzle sauce on top and garnish with green onions and tomatoes, if desired.