Brush the insides of the english muffins with olive oil. You can season the english muffin with salt and pepper, or with garlic salt and pepper, if desired. Distribute the spinach mixture evenly across the english muffins. Combine the mozzarella and parmesan cheeses and sprinkle over the mini pizzas. Top with the shrimp and cherry tomatoes. Season with salt and pepper to taste, if desired.