Pour 1 tbsp Japanese soy sauce (koikuchi shoyu), 1 tbsp mirin and ½ tsp sugar into a small saucepan and heat over medium. Let it bubble for 30 seconds, then remove from the heat.
Pour the contents of the pan into a heatproof jug or bowl, then slowly pour in the ½ tbsp toasted sesame oil and ½ tbsp olive oil while whisking vigorously. Once emulsified, add ½ tbsp toasted white sesame seeds, ½ tsp garlic paste, ½ tsp lemon juice and 1 pinch ground white pepper. Mix and store in the fridge until use.
Place 30 g baby leaf spinach and 150 g mixed leaf lettuce in a large salad bowl. Cube 1 avocado and half 100 g mini tomatoes, then scatter them around the bowl.
Arrange 200 g sashimi-grade fish on the top. Whisk or shake the dressing vigorously before use. Pour the dressing over the salad right before serving, mix gently but thoroughly, and enjoy!
Notes
Scatter the avocado, do not stir it: Cube the avocado and scatter the pieces around the bowl. Stirred into the dressing, the cell walls break and you get brown cream smeared across the leaves.Measure the sugar exactly: The dressing carries 1/2 teaspoon of sugar against 1 tablespoon each of soy and mirin. Even an extra pinch tips the dressing into a bit too sweet.Whisk to emulsify, shake the jar if it splits: A finished dressing turns cloudy and uniform when the oils break into the soy base. If it splits in the fridge after a few minutes, shake the jar vigorously before each pour.Sashimi-grade label is essential: Buy fish labeled "sashimi-grade" or "sushi-grade" only.