Preheat broiler. Place spinach in large heatproof bowl; pour boiling water overtop to barely cover. Let stand 5 min. until leaves are wilted. Drain and cool slightly. Squeeze out excess moisture. Finely chop spinach; set aside.
Meanwhile, sprinkle a bed of coarse salt into a baking dish (the salt is for holding the oysters upright). Shuck oysters, keeping them in their half-shells along with the oyster liquor. Nestle oysters into the salt. Keep chilled.
Melt butter in skillet over medium heat. Add shallot; cook 2 min. until starting to soften. Stir in flour; cook another 2 min. Stir in cream; bring to a boil. Cook 3 to 5 min. until sauce thickens slightly. Mix in reserved spinach, lemon zest and juice. Remove from heat. Stir in Swiss cheese.
Spread 1 tbsp (15 mL) spinach mixture onto each oyster. Stir together breadcrumbs and Parmesan; sprinkle overtop. Fill and top all oysters. Broil 2 to 3 min., or until breadcrumbs are golden brown and cheese is bubbling. Serve with lemon wedges.
Make fresh breadcrumbs by pulsing crusty white bread in food processor to coarse crumbs.
Serve with your favourite hot sauce.