Meanwhile, heat oil in a large, high-sided skillet over medium. Add garlic and crushed red pepper; cook, stirring occasionally, until fragrant, about 1 minute. Add wine and lemon slices; bring to a gentle simmer over medium. Add mussels; cover and cook, undisturbed, until mussels open, about 5 minutes. Remove from heat. Transfer mussels to a large bowl using a slotted spoon, discarding any mussels that did not open; reserve broth in skillet. If desired, remove mussel meat from shells, and place in a small bowl; discard shells if not using.