Preheat the oven to 200 degrees C (390 degrees F) and line a baking sheet with greased foil.
Heat the oil in a large skillet and saute the garlic for a minute. Add the mushrooms
and peppers and cook until slightly soft. Add the Swiss chard, thyme
and lemon zest
and cook until wilted. Season with salt and pepper and leave to cool slightly.
Make a lengthwise slit in the fish fillets
(keeping both ends intact) to make room for the stuffing
. Stuff half of the stuffing into each fillet and place on the prepared baking sheet. Bake for 10 minutes. Add the sugar
snaps and bake until the fish flakes easily when tested with a fork, for a further 2 minutes of cooking; the fish should still be pink inside.
Transfer to a serving platter and finish with a squeeze of lemon juice