In a roasting pan toss mushrooms with new potatoes, drizzle in garlic olive oil and toss well. Place in oven and bake 10 minutes, mix well and bake another 15 minutes.
Meanwhile, make pesto and cover top of fish fillet with pesto.
Remove roasting pan from oven, add asparagus and toss well. Make a hole in the center of the vegetables and place fish fillet in center. Put roasting pan back in the oven and bake 15 minutes.
Test fish to make sure it is cooked in the middle (trout cooks faster than salmon which cooks faster than halibut), if not bake another 3 – 5 minutes or until done.