Preheat the oven to 400°F.
Arrange the potatoes and fennel on a sheet pan, toss with oil, salt and pepper, and roast for 15-18 minutes, until soft in the center and crisp on the edges.
In a large bowl, whisk together the lemon juice, honey, garlic, mayonnaise, basil, oregano and mustard. Fold in the potatoes, fennel, scallions and season with salt and pepper.
For the salmon, whisk together the mustard, lemon juice, salt and pepper.
Arrange the salmon on a baking sheet and cover with Dijon sauce. Roast for 12-15 minutes, until cooked through.
Whisk together the tartar sauce ingredients in a small bowl.
To serve, divide the potato salad and salmon between plates. Garnish with tartar sauce, arugula and fresh dill.