In a large bowl, mix together cauliflower and olive oil until coated, then stir in 1/2 teaspoon salt and Chinese five spice to coat.
Spread on a rimmed baking sheet and bake for 20-25 minutes, until the edges are browned and caramelized.
Meanwhile, whisk together mayonnaise, minced garlic, lemon juice, remaining 1/4 teaspoon salt, and cracked pepper. Taste and adjust salt and pepper, if needed.