Preheat your oven to 400°F (200°C) and line a small baking sheet with parchment paper.
Dice the Yukon gold potato into 1/2-inch cubes and place them in a mixing bowl.
Mince the garlic clove and add it to the potatoes along with the dried thyme, dried rosemary, sea salt, and black pepper.
Toss the potatoes thoroughly (use a teaspoon of the fat from the duck confit packaging if they need moisture) and spread them in a single layer on the baking sheet.
Roast the potatoes for 20-25 minutes, tossing halfway through, until they are golden brown and tender.
While the potatoes roast, place the duck leg confit skin-side down in a cold cast-iron or heavy-bottomed skillet.
Turn the heat to medium and allow the fat to render slowly, crisping the skin for about 8-10 minutes without moving it.
Once the skin is deeply golden and very crispy, flip the duck leg and cook for an additional 2-3 minutes to ensure it is heated through.
In a small bowl, toss the fresh arugula with the lemon juice.
Plate the crispy duck leg over the roasted potatoes and serve immediately with the bright arugula salad on the side.