Basil Pesto Pizza

Name: Basil Pesto Pizza
Ingredients: 4 tablespoons plus 1 cup olive oil; 4 medium sweet onions, such as Vidalia, thinly sliced; 6 tablespoons whole raw walnuts; 2/3 cup grated Parmesan, plus more for sprinkling, optional; 1/4 cup freshly squeezed lemon juice (about 1 lemon); 4 to 5 cloves garlic, smashed; Sea salt; 4 cups roughly chopped fresh basil; 2 cups loosely packed fresh spinach; 1 cup finely chopped Kalamata olives; 1 tablespoon balsamic vinegar; 2 family-size unbaked pizza crusts, white or whole wheat; 3 medium tomatoes, thinly sliced