By skipping the sodium-laden meats, we pack a full serving of vegetables into each square, thereby doubling the fiber of most pizza chain offerings. Still every bit as satisfying as its meaty counterparts, our pie will delight even the most devout of carnivores. The dough develops a focaccia-like texture from a 24-hour resting period in the refrigerator.
1 cup warm water (100°F to 110°F), divided
5.4 ounces bread flour (1 1/4 cups)
5 ounces white whole-wheat flour (about 1 1/4 cups)
1 (1/4-oz.) envelope active dry yeast
1/4 cup olive oil, divided
3/4 teaspoon kosher salt, divided
1 Japanese eggplant, cut into 1/4-in.-thick slices
Place 3/4 cup warm water in the bowl of an electric stand mixer fitted with the dough hook attachment. Add flours; mix on medium speed until combined, about 20 seconds. Cover, and let mixture stand 20 minutes.
In a small bowl, mix yeast and remaining 1/4 cup water; let stand until bubbly, about 5 minutes. Add yeast mixture, 1 tablespoon oil, and 1/2 teaspoon salt to flour mixture; mix until a soft dough forms. Place dough in a large bowl coated with cooking spray; place plastic wrap coated with cooking spray directly on surface of dough. Chill 24 hours.
Let dough stand 1 hour, covered, until dough reaches room temperature. Place dough on a lightly floured surface; roll into a 14- x 11-inch rectangle. Press dough into bottom and partially up sides of a 13- x 9-inch metal baking pan coated with cooking spray.
Place a baking sheet in oven on bottom rack. Preheat oven to 450°F. (Do not remove baking sheet while oven preheats.)
Toss together eggplant, zucchini, squash, 1 1/2 teaspoons oil, and remaining 1/4 teaspoon salt on a separate rimmed baking sheet; spread in a single layer. Bake at 450°F for 15 minutes or until tender, turning once halfway through.
Heat 1 1/2 teaspoons oil in a large nonstick skillet over medium-high. Add onion and bell pepper. Cook, stirring often, until tender, about 4 to 5 minutes.
Spread pizza sauce over dough, leaving a 1/2-inch border; top evenly with spinach. Sprinkle mozzarella over spinach. Arrange eggplant, zucchini, and squash slices alternately over cheese. Top evenly with onion and bell pepper mixture. Brush remaining 2 tablespoons oil over dough border. Place baking pan on preheated baking sheet; move to middle oven rack. Bake at 450°F for 22 to 23 minutes. Cut into 6 squares.