Swordfish Steaks with Asparagus and Frisée Salad

Name: Swordfish Steaks with Asparagus and Frisée Salad
Ingredients: 3 Tbsp. plus 1/4 cup extra-virgin olive oil; 1 lb. asparagus, trimmed, cut into 2 1/2 pieces; 3 1/2 tsp. kosher salt, divided; 4 (1-thick) swordfish steaks (about 1 1/2 lb. total); 1 Tbsp. herbes de Provence; 1 Tbsp. Dijon mustard; 1 Tbsp. red wine vinegar; 1/2 lemon; 3/4 tsp. freshly ground black pepper, divided; 8 cups torn frisée; 3 medium Persian cucumbers, thinly sliced into rounds; 1/2 small white onion, very thinly sliced into rings, rinsed