Preheat oven to 500°. Heat the oil in a skillet over medium-low heat. Add the greens and garlic and sauté over medium-low heat until soft and slightly wilted. Remove from heat and set aside. Prepare pizza crust, as directed, and transfer to a rimless cookie sheet. Drizzle crust with olive oil and sprinkle with salt and pepper. Spread the ricotta over the pizza crust. Arrange the eggplant, zucchini, and squash in a single layer on the crust. Arrange the mozzarella slices on top of the vegetables. Place pizza in oven and bake 6 minutes. Scatter mustard greens over pizza and crack egg onto the center of pizza, if using. Return to oven for about 6 minutes longer, or until the crust is golden, the cheese is bubbly, and the egg has cooked. Transfer to a cutting board; slice and serve hot.