While shells are cooking, melt margarine in 12-inch nonstick skillet over medium-high heat. Cook onion and bell pepper in margarine 2 to 3 minutes, stirring occasionally, until crisp-tender. Stir in asparagus. Cover and cook 3 to 5 minutes,
stirring occasionally, until asparagus is crisp-tender; remove from heat. Stir in shrimp, crabmeat, 1/2 cup of the pasta sauce and half of the basil.