If using an outdoor grill, preheat the grill to medium-high heat. If using a grill pan, heat when ready to cook over medium-high heat. If using your oven, position a rack in the upper third of your oven and preheat to 400°F.
On a sheet pan, combine the mushrooms and asparagus with a large drizzle of avocado oil (enough to nicely coat the veggies), the garlic powder, and a big pinch of Kosher salt and freshly ground black pepper.
Grill the portobellos for 12-15 minutes, flipping in between and as needed, until charred and tender. Grill the asparagus for 5-8 minutes, flipping as needed, until charred and cooked through. You still want them to have a slight bite to them, they shouldn’t be totally flimsy. Transfer them back to the sheet pan and let cool to room temperature.
If using your oven, prepare a parchment-lined baking sheet. Add portobellos first. After 5 minutes, add asparagus, and roast for an additional 12-15 minutes, until both vegetables are tender. Let cool to room temperature.
Cut the portobellos in half, then thinly slice them crosswise. Cut the asparagus into 1 ½ inch pieces.
In a salad bowl, combine the arugula, ¾ of the walnuts, ¾ of the goat cheese, grilled portobello mushrooms, and the asparagus. Toss with as much of the Basil Vinaigrette as you’d like and season with kosher salt and freshly ground black pepper, if needed. Sprinkle the remaining walnuts and goat cheese on top and serve.