Put spinach, walnuts, garlic clove, Parmesan cheese, lemon juice, 1 tablespoon olive oil, and a dash of salt into a food processor; pulse, scraping down sides of bowl, until smooth. Transfer the pesto to a bowl; cover and chill. Combine paprika, dark brown sugar, crushed red pepper, 1/4 teaspoon salt, and black pepper in a small bowl. Pat dry salmon fillets; sprinkle tops with spice mixture. Heat 1 1/2 teaspoons olive oil in a nonstick skillet over medium-high heat. Reduce heat to medium; cook fish 7 minutes on both sides or until golden and cooked through. Split rolls in half; spread 1 tablespoon pesto on each bottom, and top with 1 fillet and 1 radicchio leaf. Add tops of rolls. Serve with extra pesto.