Toast the sunflower seeds in a small nonstick pan for a couple of minutes until lightly browned and fragrant. Don't burn them please.
Remove and reserve the juice from 1 of the oranges with a juicer or one of those handheld juicing tools. Peel the other orange and cut the sections into bite-sized pieces.
To Make the Vinaigrette
Combine the fresh orange juice with scallions and season with salt & pepper.
Slowly whisk in the olive oil a little at a time until emulsified. Taste and adjust amounts while you are adding the olive oil for balance.
Assemble the Salad
In a large salad bowl, combine the watercress, orange pieces, parsnip matchsticks and sunflower seeds.
Add a little of the vinaigrette and toss well to coat the watercress leaves with dressing.
Taste and adjust salad with more dressing if needed and salt & pepper to taste.