Heat a large frying pan over a medium heat. Add ½ tbsp oil along with the sausages and onion wedges. Cook for 25 minutes, turning everything regularly, until the sausages are cooked through and the onions are starting to brown at the edges.
Meanwhile, put the potatoes in a large pan, cover with water and bring to the boil. Cook for 8-10 minutes until tender. Drain.
Put the lemon juice, remaining oil, mustard and honey in a small bowl. Season and whisk to combine.
Transfer the sausages to a chopping board and cut into bite-size pieces. Tip back into the pan with onions. Add the potatoes and chopped tomatoes and gently toss together. Divide between 4 bowls along with the salad, then drizzle with the dressing and serve.