Preheat your broiler on low. Slice the French baguette into ½-inch thick pieces and arrange on a baking sheet. Broil for 3–5 minutes until lightly browned, flipping halfway through.

In a skillet, heat olive oil over medium heat. Add shrimp, onion, and celery. Sauté for about 1 minute until shrimp turns pink.

Add minced garlic, Cajun seasoning, and black pepper. Continue to cook for an additional minute, stirring constantly.

Lower the heat and add cream cheese, Parmesan cheese, and Fontina cheese. Stir until cheeses are melted and mixed well.

Evenly distribute the shrimp mixture over the toasted baguette slices on the baking sheet. Sprinkle with crushed red pepper if desired.

Preheat oven to 400°F (200°C) and bake the shrimp toast for about 10 minutes until golden and bubbly.

Let cool slightly before serving. Garnish with green onions and serve immediately.