For the pomegranate molasses: In a small saucepan, bring the pomegranate juice, maple sugar and lemon juice to a slight boil over medium-high heat. Reduce the heat to low and simmer until syrupy, about 30 minutes. Remove from the heat and set aside.
For the burgers: In a large pan, heat 1 tablespoon oil over medium heat. Add the onion and cook until softened, about 5 minutes. Add the mushrooms, carrot and celery and cook, stirring occasionally, until the liquid from the mushrooms has evaporated, about 10 minutes. Transfer to a large bowl and let cool about 10 minutes. Stir in the rice, oats, walnuts, flour and 1/2 teaspoon salt. Transfer to a food processor and pulse until coarsely combined and the mixture just holds its shape when pressed, adding water, 1 tablespoon at a time, if necessary. Shape the mixture into 4 patties.
Stir together the ketchup with 2 tablespoons of the pomegranate molasses and set aside. Heat the remaining tablespoon olive oil in a large pan over medium-high heat and cook the patties until golden, turning once, about 8 minutes total. Arrange 4 English muffin halves on plates, if using, and top with some pomegranate ketchup, the patties, spinach leaves, carrots, pomegranate seeds, more ketchup and the remaining English muffin halves.
Recipe courtesy of Silvana Nardone