Preheat the oven to 375°F (190°C). Spread the breadcrumbs on a plate and leave them to dry a little while preparing the rest of the ingredients.
Cut the tops off the peppers and scoop out the seeds and membranes. Blanch the peppers and their tops in boiling water for 1 minute. Lift out the peppers with a slotted spoon, then drain, cut-side down, on paper towel.
Heat the oil in a large frying pan over a medium heat. Add the onion and cook for 10 minutes, stirring frequently, until softened. Increase the heat, add the beef and garlic and fry, stirring, until browned and crumbly. Add the tomatoes, herbs and 1⁄4 cup of the stock. Cook for a further minute, then remove from the heat and stir in the breadcrumbs. Season to taste.
Stand the peppers upright in a lightly oiled, large ovenproof dish, fill with the beef mixture and press down gently. Sprinkle with the cheese and replace the tops. Scatter the fennel around the peppers and pour in the rest of the stock.
Cover the dish with foil and bake for 40 minutes until the peppers and fennel are tender, basting halfway through with the stock. Serve hot or warm.
Variation: Use the beef mixture to fill 4 large zucchini (about 200 grams/7 oz each). Halve them lengthwise and scoop out the centres with a teaspoon. Fill with the beef mixture. Arrange the zucchini in a baking dish, sprinkle with the cheese, then cover with foil and bake for 40 minutes. Remove the foil and bake for 10 minutes.
Per serving: 414 calories, 17 g fat (6.5 g saturated), 34 g protein, 25.5 g carbohydrates, 10.5 g fibre