Make the vinaigrette: mash the chopped plums with a fork or blend briefly until mostly smooth. Whisk in the olive oil, vinegar, honey, mustard and a pinch of salt and pepper. Taste and adjust.
Using a vegetable peeler, shave the carrots and zucchini lengthwise into long, thin ribbons. Stop when you reach the zucchini seeds or it becomes hard to hold the carrot.
Slice the radishes as thinly as you can with a sharp knife or a mandoline.
Arrange the greens on a platter and top with the ribbons and radish slices.
Drizzle with the vinaigrette, scatter over the microgreens and sunflower seeds, and serve right away.