Preheat oven to broil with rack set to the highest level.
In a small saucepan, combine butter, olive oil, garlic, shallot, and Cajun seasoning. Heat over high heat, stirring occasionally, until garlic is softened. Taste for seasoning, and add salt, pepper, and Cajun seasoning, if necessary. Remove from heat, and add parsley, stirring to combine.
If using a baking dish with wells, divide oysters among wells, with 1 or 2 oysters per well. Butter may spill over, so place baking dish on a rimmed baking sheet. Add a large spoonful of butter mixture to each well.
Broil oysters, checking for hot spots every 30 seconds, until mixture is bubbling, about 2 minutes. Top with Gouda, and broil until cheese is melted, 1 to 2 minutes more. Squeeze lemon juice over oysters. Let cool slightly, and serve with crusty bread.
Recipe by Louisiana Cookin' at https://louisianacookin.com/cheesy-herbed-broiled-oysters/