Preheat the oven to 200 ºC. Wash and halve the potatoes. Cut the peppers in half, remove the seeds and cut them into large strips. Peel and slice the onions. Peel and finely chop the garlic.
Mix the vegetables and potato with garlic and olive oil, salt and pepper and chopped rosemary.
Divide the vegetables well spread on a large baking tray and roast for about 35 minutes until cooked and colored. (If necessary, use the oven-grill for the last 5 minutes to color even more).
Grill the sausages in a grill pan (or BBQ) over medium heat for about 8 minutes until brown and cooked. Put the sausages between the vegetables in the oven for another 5 minutes.