Lay 2 good sized pieces of heavy duty foil crosswise to each other, then spray generously with nonstick cooking spray.
Place a slice or two of lemon in the center of the aluminum foil, top with a sprig of dill, then one piece of salmon.
Lightly spray the top of the salmon with olive oil spray, then season with a little garlic powder, onion powder, salt and pepper.
Place a sprig or two of fresh dill (or more - we love fresh dill!) on top of each salmon portion, then top with another half slice of lemon.
Fold foil ends in, rolling to form a well sealed packet, leaving room above and to the sides of the salmon. (See photos in the post, for how I do it.) Repeat for remaining salmon portions.
Place the salmon foil packets over your fire or grill, cook for 5-7 minutes. (5 if you like your asparagus soft, 7 if you like the asparagus crunchy).
Remove the salmon packets from the heat.
Divide the asparagus spears between the foil packets. For each packet, divide that packet’s portion of asparagus on either side of the salmon.
Add a tablespoon of butter to each packet - I cut them in half and put one half over each asparagus section. Season asparagus with a little salt and pepper to taste - you can also do the onion and garlic powder, if you like.
Re-wrap the foil packet and return to the heat.
Cook until salmon flakes easily (Internal temperature of 145 F when an instant read thermometer is inserted into the thickest part of the salmon- if you’re one to measure!), and the asparagus is as done as you like.
Actual cooking time will depend on your grill, and the thickness of your salmon, but expect about another 5-10 minutes. (Usually about 10-15 minutes total)
Carefully open each foil packet, and serve hot!