Preheat the oven to 400 degrees. Line a sheet pan with parchment paper and set aside.
Put the peeled and cut potatoes in a pot with 1 tsp salt, ½ tsp fennel seeds and enough water to cover by one inch. Bring to a boil, then reduce heat and simmer for about 5 minutes. Strain the potatoes from the water and transfer to a large bowl or back into the pot (to reduce the dishes to wash later!)
While the potatoes are boiling, cut the peppers, onions and sausage.
Toss the boiled and strained potatoes with 3 tbsp olive oil and ½ tsp salt. Spread in one layer on the prepared sheet pan. Bake for 15 minutes in the oven.
Meanwhile toss the sliced peppers, onions and sausage with 1 tbsp olive oil. Set aside.
When the potatoes are golden (about 15 minutes) remove the pan from the oven and push the potatoes to one side of the pan and add the sausage mixture.
Bake for another 10 minutes until the sausage is cooked through. If you want the potatoes, veggies and sausage to be more golden, you can broil them for 2-3 minutes.