Start by prepping all your vegetables: cut the bell peppers into 1-inch chunks, slice the zucchini and yellow squash into 1/2-inch half-moons, cut the asparagus into 2-inch pieces, and cut the onion into 1-inch wedges. While prepping, make your marinade by whisking together the red wine vinegar, 2 tablespoons balsamic vinegar, Dijon mustard, and olive oil in a small bowl until the mustard helps emulsify the oil. Add the dried basil, dried oregano, garlic powder, and season generously with kosher salt and freshly ground black pepper. I like to taste the marinade before using it—it should be tangy and herbaceous with a good balance of acidity and richness.
Place all the prepped vegetables in a large bowl and pour the marinade over them, tossing everything together to coat evenly. Let the vegetables sit at room temperature for at least 15 minutes so the flavors can start to infuse, or refrigerate for several hours if you're planning ahead. The marinade will help soften the vegetables slightly and season them throughout.
Preheat your grill to medium-high heat (around 400°F if using a gas grill). Using tongs or a slotted spoon, transfer the marinated vegetables to the grill, allowing excess marinade to drip back into the bowl—reserve any remaining marinade for drizzling later. Spread the vegetables in a single layer and let them cook undisturbed for 4-5 minutes until you see nice caramelization and char marks on the bottom. Flip the vegetables and grill for another 4-5 minutes until they're tender with charred edges. I find that keeping the vegetables from moving around too much helps develop that beautiful golden color and deepens the flavors.
Transfer the grilled vegetables to a serving platter or individual plates while they're still warm. Drizzle the reserved marinade and the 2 tablespoons of finishing balsamic vinegar over the top—the balsamic adds a final sweet and tangy note that brightens everything. Finally, crumble the goat cheese generously over the warm vegetables. The heat from the vegetables will slightly soften the cheese, creating pockets of creamy tang throughout the dish.