Heat 2 tablespoons olive oil in a medium saucepan over medium heat. Add the ginger, garlic, shallot, curry powder and 1/2 teaspoon paprika; cook, stirring often, until the shallot is soft, about 3 minutes. Add the bell pepper and cook until slightly softened, 2 minutes. Add the lentils, 1/2 teaspoon salt and 2 1/2 cups water; increase the heat to medium high and bring to a simmer. Partially cover and cook, stirring often and adjusting the heat to maintain a simmer, until the lentils are tender, about 15 minutes. Uncover and simmer until thick, 5 to 10 more minutes. Add lemon juice and salt to taste.
Preheat the broiler. Put the salmon on a foil-lined baking sheet, skin-side down. Sprinkle with 1/2 teaspoon salt and the remaining 1 teaspoon paprika and broil until just cooked through, 6 to 8 minutes.
Toss the arugula with the remaining 1 tablespoon olive oil, and salt and lemon juice to taste. Serve with the lentils and salmon.