Preheat oven to 425 degrees. Line two sheet pans with parchment paper.
Combine butter, miso and garlic in a small bowl and mix with a rubber spatula until it is well combined.
On one sheet pan, place the sweet potatoes and drizzle with 2 tbsp melted coconut oil. Toss to coat the sweet potatoes in the oil.
On the second sheet pan, place the salmon on one side and the asparagus on the other side. Spread the miso butter mixture over the top and sides of the salmon as well as on the asparagus. You can even leave little dollops of the miso-butter mixture all over the tops of the asparagus so it melts as it cooks.
Place both sheet pans in the preheated oven.
After 10 minutes, check the salmon and asparagus. If the salmon is cooked through, remove the sheet pan.
Continue cooking the sweet potatoes for 10 more minutes or until tender and golden.
Remove from the oven and serve.