Cook potatoes in a saucepan of salted water for 10 minutes, until tender. Set aside and slice when cool.
Meanwhile, lightly spray a large frying pan with oil and heat on high. Cook garlic and spinach for 2 minutes, stirring until wilted. Drain and chop coarsely. Combine spinach mixture with ricotta and season to taste.
Place pita under a hot grill for 1 minute, until crisp. Turn pita over and top with potato and spinach mixture. Sprinkle with mozzarella and grill for 2 minutes, until mozzarella melts. Serve with a mixed green leaf salad.