In two different saucepans, boil the red and yellow beets.
Add salt and cover with cold water.
Grate the zest of one orange. Set aside.
With a sharp knife, cut away the peel and pith from the oranges, exposing the flesh.
Extract the wedges (segments without the membrane), running a sharp knife between each orange wedge to separate the flesh of the fruit from the membrane. Set aside
In a bowl, crush the flesh from one orange to obtain a pulpy juice.
Season with salt and pepper.
Add the green onions, the orange zest and the mustard. Stir well.
Drizzle olive oil over while stirring to make a vinaigrette.
Cut the beets into 5 to 10 mm (1/4 to 1/2 in.) slices.
Place the beet slices in a bowl and top with vinaigrette.
Add the orange wedges from the remaining orange. Stir gently.