Rinse and pat beef cuts dry, transfer to a bowl.
Add in the oyster sauce, 2 Tbsp of soy sauce, oregano, salt, black pepper and paprika. Combine and set aside to sit for at least 2 hours.
Heat up large skillet, toss in the unsalted butter and let it melt completely.
Add in the marinated beef and let it sear on high heat for 3-5, then reduce the heat and keep tossing around with a spatula so it browns nicely.
In a bowl, combine the rest of the soy sauce and the cornstarch. If too thick, you can add 1-2 tbsp of water, mix until cornstarch is well dissolved.
Pour in the slurry into the skillet, cover and let it simmer on medium to low heat. It should begin to thicken in 5 minutes of cooking slowly.
Adjust the seasoning if needed and turn off the heat when beef cuts have tenderized to your liking.
Serve hot or warm with some rice or mashed potatoes.