Cook the fettuccine according to the package directions and drain. Meanwhile, heat the olive oil in a large nonstick skillet over medium-high heat until hot. Add 1/2 tablespoon butter and swirl until melted. Add the salmon. Cook for 4 to 5 minutes or until golden brown, turning once. Remove the salmon to a plate. Add the mushrooms and remaining 1/2 tablespoon butter. Cook for 2 to 3 minutes or until browned. Stir in the cherry tomatoes and garlic. Cook for 1 minute or until slightly softened. Stir in the spinach and cook for 30 seconds. Place the vegetables on a plate. Increase the heat to high. Add the seafood stock. Boil until reduced by half. Stir in the cream and lemon juice. Cook the sauce until slightly thickened. Reduce the heat to medium, stir in the sour cream, salt and pepper. Return the salmon and vegetables to the skillet and cook until warm. Serve over the fettuccine.