Place a large piece of parchment paper on a baking sheet. Lay the green beans and mushrooms in a pile on the center of the paper. Lay the filet of fish on top.
Top with garlic, 1/2 cup of marinara, 2 slices of lemon, a sprinkle of fresh salt, a few cracks of fresh pepper, and a sprinkle of olives and/or capers. Top with fresh basil.
Wrap the paper over the fish lengthwise, and then roll the ends towards the center to secure the paper tightly closed. Keep the packet on the baking sheet.
Place baking sheet in the oven, and bake for 18-24 minutes, depending on how thick your fish filet is. Thicker filets may need more time. It’s done when the flesh flakes at the prod of a fork.
Remove the baking sheet from the oven and let rest for 2-3 minutes. Unravel the packets and top with more herbs and lemon, if desired.