Preheat your oven to 350°F (175°C). Cut two medium tomatoes in half, and place cut-side down in a small ceramic dish. Drizzle olive oil over the top, and sprinkle with kosher salt. Roast for about 20 minutes, or until much of the water has cooked out and the flavor is concentrated. Set aside to cool.
Step 2
Cut each croissant in half, and spread each side evenly with aioli. Set aside.
Step 3
In a medium sauté pan, layer the turkey in two small stacks. Top each with spinach and gruyère. Cover, and warm over medium heat until the cheese has melted thoroughly.
Step 4
Place the roasted tomato on the bottom half of each croissant. Top with the turkey, spinach, and cheese. Serve immediately.