Preheat oven to 400F. Lay out two large squares of foil and divide the spinach between the two equally, placing it in the middle of each square.
On a chopping board, lay out the halibut steaks. There is a membrane running down the middle of each steak, along with a small bone that need to be removed. Run a small knife between the flesh and the membrane, separating each side of the steak away from both membrane and bone. Each steak should now be divided into two separate pieces of fish, so that you have four pieces in total.
Lay two pieces of halibut on top of each pile of spinach. Squeeze the lemon juice over the fillets, season to taste with smoked paprika and top each one with a slice of lemon.
Divide the sliced green onions, thai chili and cherry tomatoes equally between the two squares. Divide the avocado oil so that each piece of fish is topped with about 1/2 tbl oil.
Wrap the foil around the fish tightly & place both packages on a baking tray.
Bake for approximately 15 minutes, until fish is cooked through and flakes easily.
Remove the fish from the packages (as well as the skin from the fish if you want) and plate, spooning the juices over the fillets before serving.