- Preheat oven to 425F. Place the diced potatoes on a large sheet pan and drizzle with 1 tbsp of olive oil. Add the thyme and rosemary and then season liberally with salt, pepper, and garlic powder, to taste. Toss the potatoes with the oil and herbs and move to one half of the pan.
- Add the brussels sprouts and pepper to the other half of the sheet pan and drizzle with remaining 1 tbsp of olive oil. Season well with salt, pepper, and garlic powder. Toss to coat. Make sure all vegetables are arranged in a single layer. Bake for 15 minutes.
- Remove the pan from the oven and stir the vegetables. Place the sliced sausages on top and return to oven for another 15-20 minutes, until all vegetables are tender and golden.
- Meanwhile, prepare the mustard sauce by whisking together the dijon, mayo, lemon juice, and water. Add a pinch of salt and pepper.
Serve 1 sausage with 1/4 of the vegetables/potatoes and drizzle 2 tbsp of mustard sauce over the top. Serves 4.