Tuna Onion Poke Sauce (Mustard)

Drain the oil from the canned tuna and separate it into appropriate pieces.

Slice the onion thinly and soak it in cold water to remove the spiciness, then drain off the water.

In a bowl, mix mustard sauce, olive oil, lemon juice, salt, and pepper to make the sauce.

Place the tuna and onion in a bowl, pour the sauce, and mix evenly.