Zest the lemon and lime, then thinly slice ½ of each. Juice the other halves. Combine 2 Tablespoons of the lemon/lime juice, cumin, garlic and olive oil.
Place salmon on a sheet of parchment paper. Sprinkle with some of the lime and lemon zest, and pour the lemon-lime juice mixture over top.
Sprinkle with salt and pepper then arrange lemon and lime slices over the filet. Wrap up with the parchment paper. Place in a baking dish and bake at 350 degrees for about 15-20 minutes or until fish is flaky and done.
Mix butter, remaining juice and peel in a bowl. Microwave for a few seconds to melt.
Notes
I have also baked this salmon in a baking dish without using parchment paper. Plan on a slightly longer cook time if you don't use parchment.