Heat oven to 425°.
On a large rimmed baking sheet, toss all of the potatoes and shallots with 3 tablespoons olive oil, salt (I use 1 teaspoon kosher), and a lot freshly ground black pepper or red pepper flakes to taste.
Roast for 15 minutes, at which they’ll be barely beginning to color.
Give them a toss and add sausages. Brush the tops with a little olive oil and return the tray to the oven for another 30 to 40 minutes, until the potatoes are tender and the sausage is cooked through.
To finish: Transfer everything on the tray to a big bowl and add arugula, lemon juice, and more salt and pepper to taste.
Serve right away.
