• Wash and chop the spinach (removing any thicker stalks), cook for a few minutes until tender.
• Allow to cool, drain well and squeeze dry.
• Pre-heat oven to 180°C: 350°F: Gas 4.
• Peel and finely chop the onion.
• Grate the cheeses.
• Finely chop the parsley.
• Slice the tops off the firm tomatoes, scoop out the pulp and seeds.
• Invert on paper towels to drain, few a few minutes.
• Discard seeds, finely chop pulp and add to the spinach.
• Add the remaining ingredients, reserving some of the mozzarella cheese.
• Spoon a portion of the mixture into each of the tomatoes.
• Sprinkle with a layer of the reserved cheese.
• Place in an ovenproof dish, bake for 6-8 minutes.

If you wish you could then place them beneath a hot grill for a minute or two to brown the cheese topping.