Easy stuff here:
Prepare fish as usual (remove gills, guts, fins, tail, cut bottom jaw in half)
Prepare oven to 325.
Prepare Aluminum foil with olive oil. Lay a bed of lemon slices and place some rosemary sprigs over it. Salt and pepper.
Rub oil on your trout and make sure to get the inside of the trout lubricated. Salt and pepper the inside of trout.
Place on prepared aluminum foil.
On top of the trout add salt and pepper, add rosemary sprigs then place lemon on top.
Fold aluminum into a packet and cook in the oven. You might want to flip the aluminum packet once or twice to ensure even cooking.
Cook according to size. The thicker the fish the longer it will take.
Best results yielded by cooking directly on grill make sure it is in the middle of the oven or 1 higher if your oven doesn't have a "middle rack".
If juices start oozing out just use a cookie sheet and place the aluminum packet on top.
You can even cook it in an oven safe frying pan. Prepare the same. cover the top of the pan in aluminum.
Works for outside grills too.
This is how I cook tilapia fillets and salmon fillets.
Another recipe involves olive oil, salt, pepper, and mustard.
Lubricate fish in oil, salt and pepper, then rub mustard all over it. Place it in an aluminum foil packet and cook.