Heat a grill pan coated with cooking spray over medium-high heat. Coat the sliced rustic bread with olive oil cooking spray, then place it on the grill pan and cook until toasted on both sides for 5 minutes. Remove and cube into bite-sized pieces.
Add the olive oil to the grill pan, then place the mushrooms into the pan. Let them sit, leaving them alone, for 3-4 minutes, then flip them over for another 2 minutes, or until golden. Remove to a large bowl and set aside.
Add the asparagus and onion to the grill pan, adding cooking spray if needed. Cook, stirring often for 3-4 minutes, or until fork-tender, and add to the bowl with mushrooms.
Place the zucchini chunks and tomato quarters on the grill pan. Cook for 3-4 minutes on each side or until tender.
Gently place them into the bowl.
Add the grilled, cubed bread pieces to the bowl.
Season the veggies and bread with sea salt and freshly cracked pepper to taste, then toss to coat.
Drizzle some of the well-shaken vinaigrette on top, then toss to coat evenly. Taste & re-season or add more vinaigrette if needed.