Prepare past according to package directions in large saucepan of boiling water until al dente. Drain, reserving 1/2 cup cooking water; return to saucepan and keep warm.
Meanwhile, heat 2 teaspoons oil in medium skillet over medium heat. Add asparagus; cook 5 minutes, stirring occasionally. Add tomatoes, 1/4 teaspoon salt and 1/4 teaspoon black pepper, cover and cook over low heat 5 minutes, stirring occasionally. Add to pasta, cover to keep warm.
Combine scallops, 1 teaspoon oil, lemon juice, garlic and remaining 1/4 teaspoon black pepper in large bowl; toss to coat.
Heat remaining 1 tablespoon oil in same skillet over medium-high heat. Add scallops and remaining 1/4 teaspoon salt; cook about 3 minutes per side or until scallops are opaque.
Stir in pesto and red pepper flakes, if desired, into pasta mixture. Stir in some of reserved pasta water to make a creamy sauce. Divide pasta mixture among serving bowls; top with scallops.