Dice tomato and onion and either fry in a little oil or steam fry with 1/4 C. water until the onions are sweatted and clear. Add the whole can of tuna being careful to leave some larger pieces. Add water, salt, & pepper. Stir gently. Taste to check flavor.
We usually served it over rice! This was a coplete meal and we loved the sauce on top and as it soaked into the rice. If you have fresh mild flavor fish you can substitute (cod, flounder, tilapia) just make sure to check for bones!