Pre-heat oven to 350° F.
Pre-heat Panini press, Indoor grill, or a grill pan.
Mix together mayonnaise, basil, garlic and Dijon mustard.
Line a baking sheet with parchment paper. Place prosciutto slices in a single layer on parchment paper. Bake at 350° F for 15 minutes. Place crispy prosciutto onto a paper towel lined plate to drain some of the grease.
Place spinach in a microwave safe dish, season with salt and pepper to taste. Cook on high 5 minutes or until cooked through. Stir, and allow to cool 10 minutes or until cool enough to handle. Squeeze spinach dry.
Cut pizza crust into quarters. Trim if necessary to make 4 equal sized triangles.
Spread mayonnaise sauce on both sides of all 4 triangles. On two of the triangles, layer turkey, spinach, Artichoke hearts, thinly sliced mushroom, sliced Havarti and the crispy prosciutto. Top with remaining triangle.
Place in preheated press or grill. Cook 3 minutes. Turn ¼ turn and cook 2 minutes more to create grill marks and heat sandwich through.
Cut each triangle in half to create 4 sandwiches. Serve hot.