Line a baking sheet with parchment paper. Cut ends from tomatoes and slice each tomato into 4 wedges.
Place tomato and onion wedges on parchment. Brush with 1 teaspoon of the olive oil.
Bake 20 minutes or until edges of onion are lightly browned; set aside.
Reduce oven temperature to 375 degrees Fahrenheit.
Unroll pie crust on baking sheet. Spread mustard over crust.
Sprinkle cheese over mustard, allowing 1-inch border around crust without cheese.
Remove about 1/2 of the onion wedges from baking sheet and set aside. Arrange remaining onion and roasted tomato over cheese.
Fold 1-inch border up over tart edge. Bake for 25 minutes or until pastry crust is browned and cheese is melted.
Sprinkle tart with thyme leaves and allow to cool at least 10 minutes before cutting.
Whisk together remaining 2 teaspoons olive oil, 1 teaspoon mustard, orange juice, vinegar and salt and pepper in a small bowl. Toss dressing with salad mix and remaining onion. Cut tart into wedges and serve with salad.
Yield: 1/6 of tart plus about 3/4 cups of salad and 1/2 tablespoon of dressing, per serving.