Boil the tomatoes, remove and let cool slightly. Remove skin, cut in half, then remove seeds and cut into small cubes. Finely chop the capers. Melt the butter in a pan and sauté the thyme for a few minutes. Remove from heat, mix in the diced tomatoes and capers and let cool.
Preheat the oven to 200°C (approximately 400°F).
Combine the butter with the yogurt. Season with salt and pepper.
Warm the tortillas in the oven. Spread the yogurt, leaving a 2 cm (approximately 3/4 inch) wide margin free. Rinse and spin dry the lettuce, then cut into strips. Layer the ham and cooled tomato mixture on top. Roll up tightly and wrap in foil or a napkin. Serve immediately.