In a large pot with boiling salted water cook 16 oz fettuccini pasta until al dente. Drain. Stir in 1/4 c. pesto sauce and 2 tablespoons of olive oil. Meanwhile, in a large skillet, saute 1/2 chopped onion and 2 cloves minced garlic in 3 tablespoons olive oil until soft. Add 1 thinly sliced green bell pepper, 1/2 c. sliced mushrooms and cook until soft, about 3 minutes. Stir in 2 tbsp dry white wine, 2 tbsp lemon juice, salt and pepper to taste, and bring to a boil. Add 1 lb scallops and toss for 2 minutes. Take care not to overcook the scallops. Toss the pesto covered pasta with the scallop sauce. Sprinkle with grated Parmesan cheese. Serve immediately.