Preheat oven to 350° F. Toast Sandwich Thins® halves just to light golden. In a skillet, heat 1 tablespoon of the oil from the marinated sundried tomatoes over medium heat. Add mushrooms and cook until soft and moisture is released, about 5 to 7 minutes, and season with salt and pepper to taste. Meanwhile, pulse 5 sundried tomatoes with 2 teaspoons of their oil in food processor until smooth and add ricotta. Pulse to incorporate and season to taste with salt and pepper. Spread approximately 2 tablespoons of the sundried tomato and ricotta mixture on top of each toasted Sandwich Thins® half. Top each pizza with a few baby spinach leaves and divide mushrooms between each pizza. Place pizzas on a baking sheet and bake for 3 to 5 minutes to heat and infuse all the flavors.