1lime, 1/2 of it thinly sliced, the other half reserved for the juice
Preheat grill to 400 degrees F.
Pat salmon filets dry, and sprinkle the flesh with 1/4 teaspoon kosher salt, each. Mix softened butter with harissa powder, sriracha, garlic, and 1/2 teaspoon kosher salt.
Place a large piece of foil on the counter. In the middle of the foil, lay lime slices next to each other in similar shape as salmon.
Liberally spread all of butter onto salmon, splitting the mixture between the two filets. Then lay salmon filets over lime slices, skin side on the limes. Scatter all of the shallot over the salmon. Fold each side of the foil up and over the salmon, sealing tightly, creating a packet for the salmon to cook in.
Place the salmon onto the grill, and cook for 6-7 minutes (depending on thickness), until thickest part of salmon reaches internal temperature of 125 degrees F. You can check the salmon by moving it to the cooler part of the grill, opening the foil, and testing with thermometer. Remove from grill.
To plate, remove the salmon and shallots from the bed of lime slices, and squeeze a good amount of fresh lime juice over the top. (Don't leave the shallots on the foil, they add a lot of flavor to the bites of salmon!)
*I recommend tasting the harissa before mixing it into the butter to help you decide if you'd like to use more or less than the recipe calls for.