Cut the mentaiko lengthwise and remove the contents.

Cut the onion into wedges and dice the tomato into bite-sized pieces.

Crack the eggs into a bowl and mix. Add the mentaiko and combine well.

Heat 1 tbsp of salad oil in a frying pan over medium-high heat. Add the egg mixture and stir until semi-cooked. Remove from heat and set aside.

In the same pan, heat the remaining 1/2 tbsp of salad oil over medium heat. Add the onion and sauté until translucent. Add the tomato and stir briefly, then mix in the men-tsuyu.