Heat a small saucepan over medium-low heat. When hot, add the butter and olive oil. Add the garlic and shallots and saute until fragrant, about 30 seconds. Add the parsley, lemon zest and juice, chile pepper flakes and salt and pepper to taste. Remove from the heat.
Place the oysters on the hot grill until they pop, about 2 minutes. Carefully remove the top shells (BBQ gloves make this much easier; a thick kitchen towel is a good substitute). Spoon some sauce over top of each oyster and serve.