Heat oven to 200C/180C fan/gas 6. Arrange the peppers, cut-side up, on a baking tray. Brush with a little oil from the pack of tomatoes & mozzarella, then season. Cook for 10 mins to soften slightly.
Meanwhile, mix the couscous in a bowl with the pesto and pour over 125ml boiling water. Cover and leave for 5 mins to fluff up. Drain the tomatoes & mozzarella well, then mix into the couscous. Divide between the peppers, then sprinkle over the breadcrumbs
Bake for 15-20 mins until the top is crisp and the peppers are tender.