Combine the tomatoes and the green onions in a medium bowl.
In a small bowl, whisk together the olive oil, balsamic vinegar, Dijon mustard, orange zest, salt, and pepper until they emulsify into a thick, velvety dressing. If the dressing seems too thick, mix in a teaspoon of water.
Pour the dressing on top of the vegetables and mix to combine.
Let the salad rest for 10 minutes at room temperature before serving. This step is not mandatory but helps the flavors meld and improves the salad's flavor.
Video
Notes
The easiest way to slice scallions is with sharp kitchen scissors, as shown in the photo below. This is easier than using a knife.
Cherry tomatoes should be sliced before they are added to a salad. If left whole, they tend to slide off people's forks.
I encourage you not to omit the orange zest from the dressing. It adds a wonderful layer of freshness.
The Dijon adds flavor and helps emulsify the dressing. I don't recommend using yellow mustard in this recipe.
The 10-minute rest time is optional but highly recommended.
You can keep the leftovers in the fridge, in an airtight container, for up to three days. Take them out of the refrigerator an hour before serving them and remix the salad.