Rainbow trout is one of our favorite freshwater fish.  When we lived in Colorado Hubby would fish for these often so I was thrilled when I ran across these bad boys at HEB the other day.  I like cooking them in foil packets on the grill.  This is a super-easy and super-fast dinner!  
Rainbow Trout
Lemon Pepper
Garlic Salt
Creole Seasoning
Butter
Lemon wedge

Cut a piece of foil big enough to make a packet out.  Put fish on foil and sprinkle inside and outside of fish with all seasonings.  (I have no idea how much, just sprinkle.)  Add 3 -4 pats of butter, 1 on the inside of the fish and  2-3 on outside.  Roll foil packets up  and seal well.
Like this: 
Place on preheated grill (about 400 degrees) and cook on each side for 8-10.
Fish should be nice and flaky.
Add a squeeze of fresh lemon to cooked fish.