Scallops With Red Aguachile and Pickled Onions

Name: Scallops With Red Aguachile and Pickled Onions
Ingredients: 1 medium onion, very thinly sliced; ⅓ cup fresh lime juice; 2 tsp. dried Mexican oregano (optional); 2 dried chiles de árbol, stems and seeds removed; 4 Fresno chiles, stems and seeds removed, coarsely chopped; ½ cup fresh lime juice; 1 Tbsp. Worcestershire sauce; 2 tsp. hot sauce (preferably Tapatío); Kosher salt; 16 sea scallops, side muscle removed; 1 medium English hothouse cucumber, thinly sliced; Cilantro with tender stems and saltine crackers (for serving)