Cook pasta according to package directions, omitting salt and fat. Drain well; set aside, and keep warm.

Melt butter in a large nonstick skillet over medium heat. Add shrimp, garlic, and crushed red pepper; cook 4 minutes or until shrimp are done, stirring occasionally. Add cooked pasta, lemon juice, salt, black pepper, and spinach; cook for 3 minutes or until spinach starts to wilt, stirring to combine. Serve immediately.