In a small bowl, whisk together the lemon zest and juice, orange zest and juice, dijon mustard, parsley, and olive oil. Season to taste with salt and pepper, and set aside for now.
Next, segment the orange. Here’s how it’s done: Cut off the top and bottom of the orange to expose the flesh. Put one of the cut sides down on the cutting board, then use your knife to slice off the skin and pith off the orange. You’ll do this in sections, by slicing off one section of the skin/pith with your knife, from top to bottom of the orange, following the curve of the orange, then rotating the orange and continuing slicing off the skin until all that’s left is a beautiful skinless & pithless orange.
Next, grab a paring knife & carefully slice each segment of fruit out from it’s papery membranes. To do this, slide your knife between the left and right membranes, releasing the fruit segment in one piece. As you cut out each segment, place it in a bowl for later. Continue until all the segments are cut out of the orange. Discard the remaining membrane.
Repeat this process with the grapefruit.
Divide the baby greens into 4 salad bowls, and divide the orange and grapefruit segments on top of each. Drizzle with salad dressing and enjoy.