Preheat the oven to 400°F. Line a baking sheet with parchment paper. Place the shrimp on the baking sheet. Drizzle the tops with olive oil and sprinkle with Cajun seasoning. Toss well to coat.
Spread the shrimp out in a single layer and roast for 5 to 7 minutes, until pink. The shrimp should still be in the shape of Cs, not Os. (O for overcooked.)
If using large shrimp, cut them in halves (or in thirds) then place in a mixing bowl. If using smaller shrimp, just transfer them to the mixing bowl as-is.
Discard the parchment paper then cut the French baguette in half lengthwise, and through the center, to create four pieces. Place the baguette pieces on the baking sheet cut-side-up.
To the mixing bowl, add the mayonnaise, 1 tablespoon chopped parsley, lemon zest, and garlic powder. Toss the shrimp well, then taste and add additional Cajun seasoning if desired.
Spread the shrimp mixture over the four baguette pieces. Sprinkle a quarter cup of shredded cheese over the top of each baguette. Then sprinkle Parmesan cheese over the top of each piece as well.
Bake the shrimp toast in the oven for 5 to 8 minutes, until the cheese is melted and the edges of the bread look crusty. Remove them from the oven and sprinkle with the remaining parsley. Serve warm.
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Notes
Also, try with small scallops!Shrimp toast is best to enjoy warm and fresh from the oven. They will keep well for a day or so in the refrigerator. Reheat briefly in the oven or air fryer until the cheese has melted again. However, be aware that, while tasty, the shrimp will likely be overcooked.