Season and bake turkey breast roast. Preheat grill for medium heat and lightly oil the grill or heat skillet. Arrange asparagus, zucchini, pumpkin, red onion, and red peppers on preheated grill/skillet; cook until vegetables are tender and slightly charred, 10 – 15 minutes.
Remove vegetables from grill and cut into bite-sized pieces. Whisk olive oil, balsamic vinegar, Dijon mustard, garlic, salt, and black pepper together in a bowl to make the dressing. Toss vegetables and slices of turkey breast roast with dressing in a bowl. Serve warm or at room temperature.