Alison Roman's Overnight Focaccia, Tonight

Name: Alison Roman's Overnight Focaccia, Tonight
Cuisine: European, Italian, Mediterranean
Ingredients: 1 (1/4-ounce) packet instant dry yeast , (or 2 1/4 tsp); 2 tsp honey; 2 tbsp olive oil , plus lots more for coating the bowl and pan; 2 cups warm-ish water; 5 cups bread flour , (all-purpose flour will also do the trick here, although the dough might be slightly less elastic), plus more for the work space; 1 tsp Kosher salt; 1 small red onion , sliced into rings (about 1/8-in. tick); flaky sea salt