Make the dressing in a small bowl, whisking together the vinegar, mustard, thyme, flat leaf parsley, olive oil, and water. Whisk until well blended. Set aside.
Light a grill or preheat the broiler.
Lightly cover the tuna and squash slices with cooking spray. Sprinkle with pepper. Grill the tuna until medium rare, about 2 to 3 minutes per side. Grill the squash slices until nicely browned on both sides, about 3 to 4 minutes. Slice the tuna into thin strips.
Cook the beans in a pot of boiling water until just crisp, about 2 minutes. Drain and refresh with running cold water. Drain again.
When ready to serve, divide the greens between 4 dinner plates. Divide the green beans, squash, red bell pepper, and tomatoes decoratively on the plates and top with tuna slices.
Sprinkle each with some of the chopped olive. Whisk the dressing and drizzle over the salads.