In a medium bowl or in a jar with a tight-fitting lid, combine the balsamic vinegar, Dijon mustard, minced garlic, minced shallot (if using), honey (if using), kosher salt and black pepper. Whisk briefly to dissolve the salt and mustard into the vinegar. Slowly stream in the olive oil while whisking continuously until the dressing emulsifies and becomes slightly thickened. If using a jar, add all ingredients, secure the lid and shake vigorously until combined.

Taste and adjust seasoning. Add more salt, pepper or a touch more honey if the vinegar is too sharp. The vinaigrette can be made up to 24 hours ahead and refrigerated; bring to room temperature and re-whisk or shake before using.

Salad Assembly

Prepare vegetables: Rinse the field greens in cold water and spin or pat dry until mostly dry (excess water dilutes dressing). Halve the grape tomatoes. Slice the cucumber into 1/4" half-moons. Very thinly slice the red onion into rings; if raw onion is too strong, soak the slices in cold water for 5 minutes then drain and dry.

Combine salad components: In a large bowl, place the dried field greens. Scatter the halved grape tomatoes, cucumber slices and thin red onion over the greens. Sprinkle the parsley leaves (if using) over the top.

Dress the salad: Drizzle approximately half of the prepared balsamic vinaigrette (about 2–3 tablespoons) evenly over the salad. Gently toss with salad tongs or two large spoons until the leaves are evenly coated. Add more dressing to taste (start conservative to avoid overdressing).

Season and serve: Taste and finish with a light sprinkle of kosher salt and freshly ground black pepper as needed. Transfer to individual plates or a serving bowl and serve immediately.