Method:
Heat 1 tablespoon of the oil in a large skillet over medium-low heat. Add garlic and cook, stirring constantly, until light brown, about 3 minutes. Stir in tomatoes, sugar, parsley, basil, 1/4 teaspoon salt and 1/4 teaspoon pepper and increase heat to medium. Cook, stirring occasionally, until thickened, about 5 minutes; set aside.
Meanwhile, whisk together onion, vinegar, mustard, remaining 1/4 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Drizzle in 4 tablespoons of the remaining oil while continuing to whisk constantly; set vinaigrette aside.
Preheat grill to medium-high heat. Lightly brush both sides of pizza crust with remaining 1 tablespoon oil and transfer to grill. Turn crust often, flipping once, until just toasted all over, about 2 minutes per side. Transfer to a working surface and top with reserved tomato sauce, spreading it out to the edges. Top with half of the ricotta salata and carefully return pizza crust to grill until cheese is softened and pizza is just heated through, about 2 minutes. Transfer to a cutting board.
Toss spinach with vinaigrette, then arrange on top of pizza. Garnish with remaining ricotta salata, cut pizza into slices and serve.