Preheat oven to 400ºF. Place bread slices on a baking sheet and bake until slightly dry and light golden, 3 to 4 minutes. Cut garlic clove in half and rub 1 side of each bread slice with cut side of garlic.
In a bowl, mix Parmesan, mayonnaise, rosemary, parsley and crushed red pepper until well combined. Spread each toast with 1 generous Tbsp. of Parmesan mixture. Cut each slice into triangles. Place toasts back on baking sheet. Bake until cheese mixture is puffy and golden at edges, 7 to 8 minutes. Serve immediately.
