Pasta (Prepare 1 to 3 days ahead):

Boil pasta in salted water. Drain, rinse with cold water, and drain again. Transfer to a large bowl. Add oil and vinegars, toss lightly. Season with salt and pepper. Cover and refrigerate until serving time.

Vegetables (Prepare 1 to 2 days ahead):

Steam asparagus and broccoli separately until tender. Rinse with cold water to stop cooking process and retain bright green color. Do not cook frozen peas. Store in plastic bags in refrigerator. Mince green onions and halve cherry tomatoes. Transfer to a small bowl and refrigerate. Rinse and dry spinach leaves. Wrap in plastic and chill.

Seafood (Prepare no more than 1 day ahead):

Cut sea scallops in half. Gently poach in water about 2 minutes. Drain and rinse in cold water. Poach shrimp in their shells in the same manner until pink. Rinse in cold water. Shell and devein, then cut shrimp in half. In a bowl with scallops and shrimp, add oil, vinegars, and garlic. Set aside green onion for assembly time. Toss.

Basil Cream (Prepare 1 to 2 days ahead) - makes about 3 cups:

Combine vinegar, mustard, basil, and garlic in food processor and mix until almost smooth. With machine running, drizzle in oil. Add sour cream, whipping cream, and parsley. Puree until smooth. Season with salt and pepper. Refrigerate until shortly before serving. Stir thoroughly before pouring into serving bowl.

To Assemble:

About 30 minutes before serving, arrange spinach leaves around outer edge of a large platter. Gently toss pasta with vegetables and tomato mixture. Arrange in centre of platter with spinach as a border. Make a well in center of pasta. Drain seafood. Toss with remaining green onions and season with salt and pepper to taste. Mound in centre of pasta. Serve with basil cream.