Preheat the oven to 200°C, fan 180°C, gas 6.
Heat the oil in a large pan and cook the onion for 5 minutes until soft. Stir through the potatoes and carrots and cook for a further 5-10 minutes, stirring occasionally, until starting to brown.
Add the garlic, stock and tomatoes, and bring to a simmer. Cook for 10 minutes until the vegetables are start to soften, then pour into a baking dish. Top with the sausages and bake for 30 minutes.
Meanwhile, cook the peas in a pan of boiling water for 2-3 minutes. Drain and serve with the potato bake.
Cook's tip: for vegetarians, try swapping the chicken stock cube for a vegetable one and use veggie sausages instead of pork.