In a medium bowl, combine the vinegar, garlic, mustard, herbs, sugar, salt and pepper. Slowly whisk in the olive oil until it emulsifies. Pour half into a small pitcher and set aside.
Place the steak, tomatoes and cheese in separate zip-top bags. Divide the remaining vinaigrette into each bag. Marinate for 30 minutes. Keep the steak and tomatoes on the counter. Refrigerate the cheese.
Heat grill to medium high. Grill the steaks 4 minutes per side.
While the steak is grilling, grill the tomatoes until charred and starting to pop.
Grill the cheese 30-45 seconds per side.
Grill flatbread 30 seconds per side.
Assemble everything onto a platter. Drizzle with the remaining vinaigrette. Garnish with fresh herbs.
To enjoy, slice the steak, and serve with the flatbread, tomatoes and cheese. Drizzle with more vinaigrette.To ensure the dressing is vibrant, don't make it more than one day in advance. After a couple days, the herbs will start to dull.You can also use bottled salad dressing.