Shrimp and Fettucine with Creamy Pesto Sauce

1 (16 ounce) package linguine pasta
2 tablespoons olive oil
1 small onion, chopped
8 cloves garlic, sliced
1/2 cup butter
2 tablespoons all-purpose flour
2 cups milk
1 pinch salt
1 pinch pepper
1 1/2 cups grated Romano cheese
1 cup prepared basil pesto
1 pound cooked shrimp, peeled and de-veined, tails off
20 mushrooms, chopped
3 Roma (plum) tomato, diced

Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.

Heat olive oil in a large skillet over medium heat. Saute onion until tender and translucent. Stir in garlic and butter, and saute until garlic is soft and fragrant, about 1 minute. Disolve flour in milk (I just put mine in a tupperware container and shook it up really good), then stir in. Season with salt and pepper, and simmer 4 minutes, stirring constantly. Add cheese, and stir until melted. Stir in pesto. Add shrimp, mushrooms and tomatoes. Cook 4 minutes, or until heated through. Toss with pasta until evenly coated.