Roasted Zucchini and Eggplant Sandwich with Mashed Avocado

"Hands up if you ain’t got time for boring veggie sandwiches. These Peri Peri Roasted Veggie Sandwiches are meatless sandwich dreams come true. Veggies are garlicky, lemony, with a hint of spice - and are roasted until slightly charred. Top with mashed avocado, mayo, fresh arugula, and a fluffy bun. *drool*."